
Class "t" Li 5*4 S " 

Book 'C3 . 

Copyright^ 



COPYR5GHT DEPOSIT. 



AVIATION 



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THE MACMILLAN COMPANY 

NEW YORK • BOSTON • CHICAGO • DALLAS 
ATLANTA • SAN FRANCISCO 

MACMILLAN & CO., Limited 

LONDON • BOMBAY • CALCUTTA 
MELBOURNE 

THE MACMILLAN CO. OF CANADA, Ltd. 

TORONTO 



AVIATION 



THEORICO-PRACTICAL TEXT-BOOK 
FOR STUDENTS 



BY 
BENJAMIN M. CARMINA 

ASSISTANT CHIEF INSTRUCTOR AT THE Y. M. C. A. AIRPLANE 
MECHANICS' SCHOOL, CHARTER MEMBER AND LEC- 
TURER OF THE AERONAUTICAL SOCIETY 



N*m Ifork 
THE MACMILLAN COMPANY 

1919 

All rights reserved 



■ 4-5 
,C3 



Copyright, 1919 

By THE MACMILLAN COMPANY 

Set up and electrotyped. Published June, 1919 



■*«s 



! 9/9 



©CI.A529ia7 



& 



TO 
THE GENIUS OF MAN 

THE CORRECTOR OF NATURE 

THE CREATOR OF WINGS 
THAT BEAT BIRD AND WIND 



PREFACE 

In the compilation of this book, the guiding principle has 
been to use matter of actual theorico-practical value to the 
aviation students to enable them to work knowingly. 

For a given aeroplane part, the most common term has 
been chosen out of the maze of confusing terminology, 
which ought to have been relegated into oblivion long 
ago to facilitate the study of one of the greatest, if not 
the greatest, products of the human mind. Admittedly, 
the aeroplane is in its infancy, but an infant that can 
go at such a high rate of speed and perform such marvel- 
ous feats certainly deserves more than passing attention, 
and it is high time to standardize the names of its parts, 
at least. Although wrong as any other, the term " plane' ' 
has been used to designate a wing or a wing-like structure, 
because it is incorporated in the very word "aeroplane," 
and to have introduced a new and proper term would have 
meant the changing of even the name of the machine, thus 
creating more confusion. 

The appendix has been added for the benefit of the students 
who wish to go deeper into the science of aerodynamics, and 
to facilitate the task of those who have not the necessary 
mathematical knowledge, the superficial elements of algebra, 
trigonometry and the metric system have been given in the 
definitions. 

It is hoped that this treatise will fill the long felt want of 
a theorico-practical text-book on aviation. 

The Author. 



CONTENTS 

CHAPTER I 

Theory of flight. Planes: flat planes, cambered planes, active and 
passive drift. Stability: longitudinal stability, lateral stability, 
directional stability, inherent stability — longitudinal dihedral 
angle, lateral dihedral angle, angle of sweepback, vertical 
stabilizer, gliding angle, propeller torque 1 

CHAPTER II 

Aeroplane construction. Parts: uselage, undercarriage, center 
section, wings, empennage, wires, power plant. Controls. 
Pontoons. Materials: strength of materials, wood, metal, fab- 
ric 34 

CHAPTER III 

Rigging. Assembling: fuselage, undercarriage, center section, 
wings, empennage, control wires. Truing: fuselage, under- 
carriage, center section, wings — -lateral dihedral angle, angle of 
incidence, stagger, wash in and wash out, aileron droop — em- 
pennage, controls. Rigging care and faults 70 

CHAPTER IV 

Propellers: theory, problems, manufacture, balance, test, care, 

boss 83 

CHAPTER V 

Maintenance: inspection, forced landing, repairs: wood, metal, sol- 
dering, fabric, rubber 100 

CHAPTER VI 

Plight hints: methods of instruction, taxying, elementary flying, 

stunts 116 

APPENDIX 

Aerodynamical formulae and calculations 133 

DEFINITIONS 

Aviation glossary, algebra, metric system, trigonometry 147 

Index 167 

ix 



AVIATION 



AVIATION 

CHAPTER I 
THEORY OF FLIGHT 

Planes 

Aviation is the branch of aeronautics that treats of the 
gasless aircraft. 

The fundamental law governing aviation is based on the 
resistance of the air against a body moving through it. 

Man's first application of this law to obtain flight is found 
in the use of the kite, which is in reality the forerunner of 
the aeroplane. 

In analyzing the process of kite flying, we find that, in 
order to accomplish flight, a natural current of air must 
blow against the kite or the kite must be dragged through 
the air generating its own artificial current, and that in 
either case the kite must be at an angle with the horizon 
and not in a vertical position. While it is immaterial, there- 
fore, whether the air attacks the kite or the kite attacks the 
air, it is imperative that the kite be at an angle with the 
horizon or there will be no flight. From experience, we know 
this to be so; now let us see why. 

Flat Planes. — If we move through the air a normal plane, 
it simply pushes the air back without accomplishing any 
work, because the air meets the plane perpendicularly and 
slips off all around the edges evenly. The air pushed back 
by the plane will exercise against it a certain resistance with 
a consequent pressure, whose center will be in the center of 
figure. If we double the speed of the plane, the plane will 
displace double the amount of air and the air will strike the 
1 



2 AVIATION 

plane with double the force, so that the resultant resistance 
will be the product of two times the mass of air engaged by 
two times its striking force, that is, four times as great as 
before or equal to the first amount of resistance multiplied 
by the square of two. If we treble the speed, the plane will 
engage three times the amount of air, the air will strike the 
plane with three times the force and the result will be nine 
times greater or equal to the first amount of resistance by 
the product of three times three or the square of three; and 
so forth. We can say, therefore, that the resistance of the 
air to a normal plane moving through it is proportional 
to the surface of the plane and to the square of the velocity. 
Properly speaking, for very high speeds the resistance in- 
creases at a greater rate than the square of the velocity, 
until we reach the 5th power at about 800 miles per hour, 
when it begins to diminish until it becomes less than the 
square, but for all practical purposes, we may say that the 
square law holds good. 

If we now move through the air an inclined plane A B 
(Fig. 1), the air strikes the under side of the plane and flows 

downward perpen- 
dicularly. In so do- 
ing, while it tries to 
force the plane back- 
ward, in the mean- 
time, forces it up- 
ward. In this case, 
the center of press- 
ure P is toward the 
g * front, because the 

front part of the plane does most of the work, as it engages 
undisturbed air. We may consider this resultant force P di- 
vided in its two components L and D, the first acting in 
a vertical direction and pushing the plane upward, the second 
in a horizontal direction and pushing the plane backward. 
The vertical component is the lift and the horizontal, the drift. 




THEORY OF FLIGHT 3 

The angle a formed by the plane A B with the horizontal 
C E is the angle of incidence. If we lower the front edge of 
the plane still further until it is horizontal, then the angle 
of incidence will be zero; and if we continue to lower it still 
more, the angle formed by the plane below the horizontal 
will be a negative angle of incidence. 

The resistance of the air, against an inclined plane moving 
through it, is proportional to the surface, the square of the 
velocity and the sine of the angle of incidence. 

Flat planes do not give good results, because the air meeting 
the plane is shot down vertically and the rear part does little 
work, as it engages air which has already a downward trend, 
besides the fact that the air rushing past the entering edge 
of the plane carries away part of the air in the rear of it, 
causing a partial vacuum, which renders easier the work 
of the pressure of the air in front of the plane in pushing it 
back and resulting, therefore, in greater drift. In this con- 
nection, the arrangement of planes which deserves special 
attention is the tandem arrangement, because it explains 
the increased lift of curved planes. 

If we place three planes, equal in shape, dimension and 
inclination, one after the other in a straight line and drive 
them through the air, we find that the first plane lifts a great 
deal more than the second and the third respectively. The 
reason for this marked falling off in the lift of the rear planes 
is that they have to engage the air, which was already pushed 
downward by the preceding ones and therefore caused to 
meet the rear planes with a different horizontal velocity 
than it met the forward planes. 

It is evident that if we want to use the tandem arrange- 
ment, we have to dispose the planes so that the rear ones 
will be able to engage undisturbed air, and to do this, we 
have to place the second plane lower than the first, and the 
third lower than the second; that is, in steps. This differ- 
ence in level must be proportional to the size of the planes, 
so that the air moved by the preceding ones will pass above 



4 AVIATION 

the rear planes. The best disposition will be attained when 
the sum of all the spaces between the planes is equal to the 
whole area occupied by the planes. In this way, we will be 
able to produce a large lift per unit of surface and a relatively 
low drift. 

But we can dispose the same planes in another way, 
which is just as effective as the step formation and which, 
incidentally, leads us to the formation of the curved planes. 
Cambered Planes. — As we have just seen, an inclined 
plane, moving through the air, leaves it at the rear edge 
with a downward motion; if we, therefore, want to use two 
or more planes one after the other, we have to place the 
rear planes at a greater angle than the preceding ones, so 
as to engage the air already pushed downward by the 
latter. 

Suppose that A B (Fig. 2) is a plane inclined at an angle 
of 6°; if we drive it forward, it is clear that the air will flow 

_4 away at B with a 
downward trend; so, 
if we want to use 
another plane C D 
behind it, we will 
have to put it at a 
greater angle, say 10°, and if we want to add a third plane 
E F, we have to set it at a greater angle than the second plane, 
say 12°. As there is no reason why we should use three planes 
instead of one, which will answer the same purpose, we can 
substitute for the three planes A B, C D, E F, the plane 
A F, which will have the same shape formed by the other 
three, with the joints rounded off, so as to present a con- 
tinuously curved stream-lined surface, that is, a surface so 
shaped as to exactly follow the contour of the line traced 
by the successive positions of a particle of fluid moving ac- 
cording to a determinate law. A stream -line is a continuous 
curve, as a fluid can not instantly change its direction of 
flow without forming a detrimental surface of discontinuity, 




THEORY OF FLIGHT 5 

as is the case with flat planes. This explains partly the reason 
why curved surfaces give more lift and relatively less drift 
than flat ones; and it explains it only partly because the planes 
used to-day have a double curvature, one above and one 
below, differing in degree and imitating the conformation 
of a bird's wing. Planes so shaped were at first used in mere 
imitation of nature, as in trying to realize man's dream of 
centuries, the conquest of the air, nothing was more natural 
than to imitate the only real, living flying machine in exist- 
ence, the bird, but the attempt failed, not because the 
principle was wrong, but for the great disparity for unit 
weight between the muscular power of man and bird and 
for the multiplicity of parts needed, with the consequent 
friction, which would render uneconomical even the use of 
motors to accomplish flight through such a mechanism. 
But although the machine with the flapping wings, or orni- 
thopter, was a failure, it played a very important part in 
the solution of the problem of aerial navigation, for it re- 
vealed to us the mysteries of the conformation of the bird's 
wing, whose construction we imitate in the design of the 
successful flying machine of to-day. The revelation of this 
natural secret, coupled with the knowledge of the laws that 
govern the flight of the kite, gave us the means to conquer 
the air. 

If we move through the air a plane A B (Fig. 3), having 
an upper and lower camber as the planes used to-day, the 
leading edge A splits the air and forms two currents; one 
follows the lower camber and produces a compression, which 
resolves itself in lift and drift as in the flat plane, but, in 
the present case, it flows smoothly along the camber and 
gives the maximum lift, although the front part has more 
lift than the rear even in a cambered plane, as it engages 
always undisturbed air; the other current, striking the front 
paH of the upper camber, glances upwards and, in rushing 
to the rear, carries with it the air lying between itself and the 
upper camber, causing in this way a rarefaction perpendicu- 



AVIATION 



lar to the plane and rendering more effective the pressure 
on the lower camber, which tries to equalize the difference 




Fig. 3 

in the density of the air above and below and produces a 
greatly increased lift. The greater amount of lift is due to 
the rarefaction on the upper camber, which in some planes 
is as much as 80 per cent, the balance, or 20 per cent, being 
given by the pressure on the lower camber, while the drift 
is simply the horizontal component of this pressure. From 
this, we see clearly why cambered planes are much better 
suited than flat ones to accomplish flight. 

A very simple experi- 
ment will conclusively 
prove the lift due to the 
upper camber. 

If a sheet of paper A B 
(Fig. 4) is first folded, then 
opened, without flatten- 
ing it out, and one part 
C is laid flat on a board, 
the other part D forms a 
curve behind the line of 
the fold; if we now hold 
the flat part and by mouth 




Wind 



Fig. 4 



direct a stream of air parallel to it, the curved part rises 
and, if the current is strong, it jumps up. 

In considering the lift and drift of a plane, we have to take 
into consideration its horizontal and vertical projections or 




Fig. 5 



THEORY OF FLIGHT 7 

equivalents. The horizontal projection A C of a plane A B 
(Fig. 5) increases A C with a decrease in the angle of inci- 
dence, while its vertical projection A D decreases A D', 
and vice versa. The lift is proportional to the horizontal 
equivalent, the drift to 
the vertical equiva- 
lent. This means that 
the smaller the angle, 
the greater the lift, 
and the greater the 
angle, the greater the 
drift; but, on the other 
hand, the increase of the angle causes the plane to engage 
more air, and as in reality it is the product of the two that 
must count, that is, the surface of the plane and the mass of 
air, an increase of angle means an increase of lift besides 
an increase of drift, so that at a certain angle the two forces 
will balance. The best proportion of lift to drift, or lift 
drift ratio, is found for small angles, as, in this case, the 
proportion of the horizontal equivalent to the vertical equiv- 
alent is the highest. In other words, the nearer the plane 
comes to the vertical, the greater the drift and, consequently, 
the greater the power needed to overcome it, and vice versa; 
which means that the theory of the plane set at an angle 
is the same as the old known theory of the inclined plane. 

Let us make this clearer. If the greatest weight that a 
man can lift in a perpendicular line to a height of two feet 
is 150 pounds and he has to lift a greater weight, he usually 
resorts to the use of a plank, by putting one end of it on 
the point where he wants to raise the weight and the other 
end on the ground, and rolling on it the given weight to 
the given height. As weight means gravity, it is clear that 
in this case the power employed to lift the weight is less 
than that of gravity, and, consequently, the use of the in- 
clined plane is very economical in the expenditure of power. 
For this>very reason, the solution of the problem of aerial 



8 AVIATION 

navigation by means of the helicopter, or machine intended 
to fly by means of horizontal propellers which would raise it 
straight up from the ground, has not been possible so far, 
as such a machine, to leave the ground, must produce first 
of all a vertical force powerful enough to overcome that of 
gravity, and this without considering the power lost in con- 
sequence of the extreme fluidity of the air. Other consid- 
erations are against the use of the helicopter. Even ad- 
mitting that a motor so light and powerful could be found 
to accomplish flight by such means, it is necessary to use 
at least two propellers, because if only one were used, the 
propeller torque, or rotary force of the propeller, would cause 
the machine to revolve in an opposite direction. Then 
again, once the machine is raised from the ground, another 
propeller would be necessary to make it move in a horizontal 
direction or the machine should be tilted so that the same 
propellers that raise it, cause it to move horizontally. And 
finally, supposing that flight could be accomplished by 
means of a helicopter, there is to consider the ever present 
possibility of the stoppage of the motor, in which case the 
machine would tumble down like a plummet. In opposition 
to this and in further confirmation of the great superiority 
of the machine using the inclined plane for its sustentation 
in the air, we will cite the case of the glider used in the ex- 
perimental stages of aerial navigation, which was sufficient 
to raise into the air the weight of a man by means of his 
muscular power; and the glider was nothing but a flying 
machine without motor and propeller. 

In regard to the shape of the curvature of cambered planes, 
the best suited is the parabolic curve, with its highest point 
near the front edge. This parabola, as soon as struck by 
the air, pushes it downward with a constant vertical velocity, 
without interference with the following masses of air, in this 
way increasing the lift and decreasing the drift. 

As to the degree of curvature, no definite rule can be 
given, because it must vary according to the speed of the 



THEORY OF FLIGHT 9 

machine; the curvature being smaller, the speedier the 
machine, in order to decrease the drift. From this, it follows 
that the rule set by the great, unlucky pioneer, Lilienthal, 
that the curvature be 1/12 of the chord of the arc, can not 
be applied generally. Most likely this conclusion was 
reached through the study of bird wings, but evidently we 
could not properly compare them with the planes of a ma- 
chine, as the birds use their wings both for napping and glid- 
ing, while we use the planes for gliding only. That the same 
curvature would be successful for both cases is, therefore, 
out of the question. 

The angle of incidence of the cambered planes is of the 
greatest importance ; the plane must be set so that, in splitting 
the air, it allows the latter to flow above and below without 
disturbing its continuity. What this angle is to be, it must 
be arrived at according to the shape of the plane. 

From the foregoing, it is clear that nothing is established 
with certainty as yet in regard to cambered planes, and, 
therefore, we must be guided by actual experience to find 
the best angle of incidence and the center of pressure, which 
differ with the degree of curvature. 

Owing to the camber of the planes, it would be impossible 
to measure the angle of incidence, which would vary at dif- 
ferent points, unless some means were found to make it 
equal throughout and this is accomplished by using the 
chord or straight line A B (Fig. 6a) drawn from the leading 
to the trailing edge, but, in this case, when the angle of in- 
cidence is zero, that is, when the chord is parallel with the 
horizontal or line of flight, the plane has still lift, due to 
the upper camber and, consequently, the real zero angle for 
cambered planes must be below that given by the chord. 
This point is found by experiment in the wind tunnel by 
lowering the leading edge D (Fig. 66) of the plane, until 
it is in such a position that there is no lift. Then, a line 
C E drawn from the trailing edge through the width of the 
plane, parallel to thejine of flight, will be the neutral line. 



a 




10 AVIATION 

This, therefore, brings us to the consideration of two angles 
of incidence in a cambered plane; one B A F (Fig. Ga) formed 

by the chord A B with 
the line of flight A F, 
or rigger's angle of in- 
cidence, and the other 
G A F formed by the 
neutral line A G with 
the line of flight A F, 
or flying angle of in- 
cidence. 

For practical pur- 
Fig. 6 , ., . , 
& poses, only the rigger s 

angle of incidence is used, as the neutral line is imaginary 
and we have no means to find it unless by experiment in 
the wind tunnel, while the chord can always be found. So, 
when we say that a plane is set at a zero angle of inci- 
dence, we mean that its chord is parallel with the line of 
flight, and if the plane is said to be at a negative angle of 
incidence, it means that the chord forms an angle below the 
line of flight. 

The travel of the center of pressure in flat and cambered 
planes deserves our attention. If the front edge of a flat 
plane is lowered, the center of pressure moves forward and 
lifts the plane, and if the edge is raised, the center of pressure 
moves backward and lowers the plane. Flat planes, there- 
fore, are stable. It is not so with cambered planes, because, 
on account of the two cambers, the center of pressure is the 
resultant of two forces and, consequently, it acts differently 
than in flat planes; that is, when the leading edge of a cam- 
bered plane is lowered, the center of pressure moves back- 
ward, and if it is raised, it moves forward. From this, it is 
clear that cambered planes are unstable, because if the lead- 
ing edge rises, the center of pressure, moving forward, causes 
it to rise still more, and if it is lowered, the center of pressure 
moves backward and causes the plane to lower still more; 



THEORY OF FLIGHT 11 

but although cambered planes are unstable, they are used 
because they give greater lift and smaller drift than flat 
planes. 

Another factor of great importance entering in the con- 
sideration of lift is the proportion of the dimensions of the 
plane, that is, the ratio of length or span to width or chord, 
which constitutes its aspect ratio. The greater the propor- 
tion of span to chord, the greater the lift of the plane, because, 
as we know, the greatest part of the work is done by the 
front of the plane and again because all the air entering at 
the leading edge does not flow to the rear, but some of it is 
spilled at the lateral ends of the plane. The area of a plane, 
found by multiplying its dimensions, is not, therefore, the 
effective area, and for this reason, the plane must be much 
longer than it is wide. From this, it follows that the longer 
the plane, the better it would be in respect to lift, but of 
course there is a limit. The plane must be light and strong 
in the meantime, and we could not build a plane immensely 
long without increasing its weight beyond the limit imposed 
by the aerodynamical laws, for the reason that the volume, 
and therefore the weight, of a body increases as the cube of 
the linear dimensions, and the surface as the square of the 
dimensions, and, consequently, the relations between weight 
and surface would be completely disturbed. Therefore, it 
is better to have several superposed planes of reasonable 
dimensions, say 6 to 1, rather than one of great length. In 
regard to width, it is to be observed that while narrow planes 
give greater lift than wide ones, they do not offer the same 
safeguard in minimizing the fall of a flying machine in case 
of a compulsory glide from a height. As we see, therefore, 
there is a limit for both dimensions, span and chord. 

If the span of a plane A (Fig. 7) is 30 feet and the chord 
is 6 feet, its aspect ratio is 30: 6 = 5. If we cut it in half 
lengthwise and we put the rear half B alongside the front 
half, then the aspect ratio would be 60: 3 = 20. The former 
would be a low aspect ratio and the latter a high aspect 



12 



AVIATION 



ratio. While in both cases we have the same surface, the 
second plane would be much more efficient than the first, 



-50'- 



-50^ 



A 



Fig. 7 

because in taking the rear part of the plane, where it was 
doing very little work, and putting it in front, where it will 
do the greatest work, we have greatly increased the lift. 
Besides this, there is to consider the spill of air, which is 
halved, in the former plane taking place along two edges 
six feet long, and in the second along two edges only three 
feet long. For the same reason, if we were to turn the plane A 
so as to offer to the air the smaller side (Fig. 8), the lift 
would be immensely reduced, because of the great spill of 
air and the small section of the plane doing effective work 
ir front. In conclusion, we may say that a high aspect ratio 
is the best, but, on the other hand, it 
would be impossible to build a plane 
with a very high aspect ratio, as it 
would be necessary to increase the 
thickness of the frame work used in the 
construction of planes to such a point, 
that what we would gain in lift, we 
would lose in weight. It is for this 
reason that we resort to the grouping of 
planes in superposed fashion. By ar- 
ranging the planes in this way, we get 
about as much lift as with one long 
plane equal to the sum of their dimensions, a good saving in 
weight and great strength of construction. 

In the arrangement of superposed planes, care should be 
taken to make the gap or interplane distance at least equal 
to their width, otherwise there will be interference and the 
lift will be diminished. Interference is the detrimental effect 




Fig. 8 



THEORY OF FLIGHT 



13 



produced in the gap by the rush of air, or wash, which dis- 
turbs both the rarefaction of the top camber of the lower 
plane and the compression of the lower camber of the upper 
plane. The greater loss of lift is in the lower plane, because 
in this case it is the rarefaction which is disturbed and we 
know that it is from the rarefaction that we get the greater 





Fig. 9 

amount of lift. For parity of surface, two superposed planes 
give about 15 per cent less lift than one single plane. The 
effect of interference could be eliminated by spacing the 
planes far apart one from the other, but as wooden sticks 
or struts are used to accomplish this, they should be made 
so thick that their weight and resistance would cause a loss 
instead of a gain. The best way to diminish interference as 



14 AVIATION 

far as possible, without unduly increasing the weight, is to 
stagger the planes, that is, to dispose them in steps (Fig. 9). 
If the top plane is forward of the lower plane, the stagger is 
positive (Fig. 9a); if the position is reversed, it is negative 
(Fig. 96); and if there is no stagger at all, it is zero (Fig. 9c). 
Sometimes in superposing planes, the top one is made 
___________________________ longer (Fig. 10) as in 

this case the extension 
gives the full amount of 

lift, having no plane on 

F j g 10 the under side to pro- 

duce interference. 
Active and Passive Drift. — We have considered so far 
the best angle and disposition of the planes without men- 
tioning either the means to keep them rigidly in place to 
maintain the angle and disposition given or those to furnish 
the motive power. It is evident that a framework, an engine 
and a propeller are necessary to obtain our object. The 
embodiment of these different parts in a unit constitutes the 
aeroplane, which is, therefore, a power driven aircraft sus- 
tained in flight by the reaction of the air against planes set 
at an angle with the line of motion. It is distinguished as 
monoplane and multiplane, according to the number of 
superposed planes used; the biplane and triplane being simply 
particular cases of the multiplane. 

The shape of an aeroplane very closely resembles that of 
a bird, both having a body, legs, wings and a tail, the only 
difference being that the bird has movable wings, which 
furnish both motive power and sustentation, while the 
aeroplane has rigid wings for sustentation only and the 
power is furnished by a motor, whose rotary motion is trans- 
formed into a linear motion by means of a propeller attached 
to it. As the machine moves through the air, there is resist- 
ance against the planes as well as against the framework. 
The resistance against the planes is active, as it gives lift 
besides drift, but the resistance against the other parts is 



THEORY OF FLIGHT 



15 



all passive drift and must be overcome in order to accomplish 
flight. To diminish this passive drift as much as possible, 
the different parts used in a machine are given a special 
shape, which has been found to be the best suited for the 
purpose. 

If we move through the air a body A B C D (Fig. 11), 
having right-angled corners, the air, coming in contact with 




Fig. 11 

the front part of the body, jumps off at the corners and falls 
toward the rear, until it meets again at a certain point E. 
Between this point and the rear part of the body a vacuum 
is formed which retards the forward motion of the body. 
This is due to the fact that the air meeting the corners can 
not instantly change its direction of flow and follow the 
shape of the body. If we round the front corners, the air, 
instead of jumping off, flows gradually along the curvature 
and the sides, meeting at a nearer point F in the rear. If we 
cut the sides tapering down to a point toward the rear, 
then the air follows exactly the contour of the body, eliminat- 
ing the formation of the vacuum. The body will then be so 
shaped as to be blunt at the front part and thin at the rear. 
This is a stream-lined body and the ratio of length to width 
is its fineness. The fineness of a stream-lined body is pro- 
portional to the velocity, that is, the thinner the body the 
better suited to move through the air at a high velocity, 
because the air has less tendency to jump off in meeting the 
blunt part. If the body, instead of being rounded off at 
the front, had a sharp end, it would split the air more easily, 



16 AVIATION 

but this would be a loss instead of a gain, because when the 
air meets the blunt part and is split, it forms a vacuum C7, 
which, being in the direction of motion, is beneficial, both 
because it helps move the body forward and because of the 
saving in the weight of material by cutting off the sharp 
edge. This small vacuum in front of a stream-lined body 
is known as Phillip's coefficient. When a body can not be 
stream-lined by cutting it into shape, then additional parts 
of wood, metal or fabric are used, so as to give it the proper 
form for least resistance. 

Another factor which increases the passive drift is the 
skin friction. In regard to this point, there is a great deal 
of controversy, some authorities saying that it is due to the 
roughness of surface; others, that it is the rubbing of the air 
against the layer of air which surrounds all bodies and ad- 
heres to them even when in motion. While this point is still 
in doubt, what is positively known is that the coefficient of 
skin friction is inversely proportional to the area and the 
velocity, that is, the greater the surface and the greater the 
velocity, the smaller the amount of skin friction. 

To still diminish the passive drift, advantage is taken 
of the shielding offered by one body on another following 
in its wake within certain limits. It has been found out by 
experiment that if two disks are placed one behind the other 
and a stream of air is directed against them, by moving the 
rear disk away from the front one and noting the drift given, 
at a distance of 1.50 times the diameter of one disk, the re- 
sistance of both is a minimum or 75 per cent of that of one 
single disk; then it increases to a medium at 2.15 diameters, 
becoming equal to that of one disk; and to a maximum at 
10 diameters, equaling that of two disks. Why the resistance 
decreases instead of increasing from zero to 1.50 diameters, 
it is not very clear, but it seems that when the rear disk is 
moved backward that far, the eddy currents formed behind 
the front disk have the effect of pushing it forward with such 
a force as to diminish the backward pressure against both 



THEORY OF FLIGHT 17 

disks; past that point, the eddies have less or no effect and 
the pressure increases, as it should. 

In the practical application of the case of the disks to 
that of constructional parts, we have to take into considera- 
tion the dimensions of the sides exposed to the direction of 
motion. In other words, if the cross-sectional dimensions 
of two parts are 1 inch -by 2 inches, and they are placed 
with the 1-inch side facing the direction of motion, the dis- 
tance between them should be less than 10 inches or, if the 
other side is exposed, less than 20 inches to obtain a decrease 
in drift. 

Evidently, it is not always possible to take full or even 
partial advantage of the shielding effect, owing to construc- 
tional requirements. We can conclude, therefore, that if 
it is possible to place parts of the framework of a machine 
at distances nearer than 10 times the dimensions offered 
to the direction of motion, there will be a reduction in passive 
drift, due to the shielding effect of one part on the other. 

Stability 

Equilibrium is the state of balance produced by the mutual 
counter action of two or more forces. Equilibrium is charac- 
terized by three phases: stable, unstable and indifferent or 
neutral. A body is in a state of stable equilibrium when, 
being disturbed, it tends to return to its previous position; 
in this state, the center of gravity of the body is in its lowest 
possible place. A body is in a state of unstable equilibrium 
when, being disturbed, it tends to move away from its 
previous position; in this state, the center of gravity of 
the body is in its highest possible place. A body is in 
a state of indifferent or neutral equilibrium when it will 
keep its balance independently of the position it is put 
in; in this state, the center of gravity of the body is at its 
center. 

The best form of equilibrium is the neutral, but as it is 



18 ' AVIATION 

not always possible to attain it, the next step is to try to 
obtain the stable equilibrium. 

From the standpoint of stability, the flying machine 
differs from any other form of locomotion. Being prac- 
tically suspended in such a light and subtle fluid, as the air, 
the aeroplane is apt to move and oscillate in the direction 
of all its three axes: longitudinal, lateral and vertical; and 
consequently its stability must be considered in connection 
with these three phases; that is, the longitudinal, the lateral 
and the directional stability. The lateral stability, again, 
must be considered in regard to straight flight and circular 
flight. 

Longitudinal Stability. — To obtain longitudinal stability 
it is necessary to balance the four forces which act upon an 
aeroplane through their respective centers, that is, gravity, 
lift, resistance and thrust. If these forces were to act always 
through a common point, it would be very easy to obtain 
and maintain equilibrium, but this is impossible in an aero- 
plane. While, by a suitable disposition of the various parts 
of the machine, we can fix the center of gravity, the center 
of resistance and the center of thrust, we can not always 
bring them in line, owing to constructional requirements, 
nor always count on the thrust, which varies with the varying 
power of the motor and will be completely absent when the 
motor is stopped and gravity supplies the gliding power; 
nor can we fix the center of lift, as it changes its position 
with a change in the angle of attack. The most we can do, 
therefore, is to balance these forces for the normal angle of 
incidence of the machine and introduce other means to re- 
store the equilibrium when it is disturbed by a change of 
the angle or the stoppage of the motor. This is effected by 
additional horizontal and vertical planes placed at the rear 
of the main planes, which act either automatically or are 
controlled by the aviator. Let us suppose thai the center 
of gravity of the machine A B (Fig. 12) is at G, and that, 
when in motion, the air will exert a center of pressure at P, 



THEORY OF FLIGHT 19 

under the main plane A C. The force tends to lift the plane 
A C and to upset it. To avoid this, the horizontal plane 
D B is connected with the rear part of the machine, so that 
the same air pressure will act under it, and on account of 



Fig. 12 

its long lever arm C B, will counterbalance the force P and 
maintain the equilibrium of the machine. 

If, instead, the aeroplane dives, due to a stoppage of the 
motor or other cause, the case is reversed; the main plane 
A C falls, while the plane D B rises and the air pressure acting 
on the upper side of the plane D B, forces it down and re- 
stores the equilibrium. Usually, this additional stationary 
plane is set at no angle of incidence and has just enough lift, 
due to the upper camber, to carry its own weight and that 
of the tail, so that it is very sensitive to any change of in- 
clination. 

To further supplement this righting force or direct the 
machine up or down, a horizontal rudder is provided, which 
is manipulated by the aviator by means of a control lever. 
By increasing or diminishing the angle of incidence of the 
horizontal rudder, which brings about a corresponding mo- 
tion of the main planes, the machine is caused to rise or 
descend. 

Lateral Stability. — To maintain lateral stability in straight 
horizontal flight, the best position of the center of gravity 
is below the center of pressure. In this way, if a side gust 
of wind strikes the aeroplane, compelling it to tilt, the center 
of gravity is displaced, too, from its normal position, which 
it will tend to regain and in so doing will bring the aeroplane 
back into equilibrium. But, evidently, this is only possible 
when the power of the wind is not so strong as to upset 



20 AVIATION 

completely the resistance opposed by the center of gravity. 
In the case of a strong wind, the aeroplane, struck sideways, 
would turn turtle. 

In regard to the center of gravity below the center of 
pressure, it is to be observed that it must be neither too 
near to, nor too far from it. In the first case, the machine 
would be too sensitive to side motions; in the second case, 
there would be a swaying action which would tend to destroy 
rather than maintain equilibrium. 

An additional means for maintaining lateral equilibrium 
is the warping of the planes or manipulation of the ailerons; 
that is, the lifting of the rear extremity of one of the main 
planes or wings and the contemporaneous lowering of the 
rear extremity of the other, so as to cause a difference in the 
angle of incidence of the two wings and bring about a twisting 
motion, in order to regain the lost stability. 

Let us examine, now, the last phase of lateral stability, 
that is, circular flight. 

When an aeroplane moves in a circle, it becomes sub- 
jected to a new force: the centrifugal force, which tends to 
drive the machine away from the center of rotation. As 
this force is directly proportional to the mass by the square 
of the velocity and inversely to the radius of the circle, it is 
greater, the greater the speed and the smaller the radius of 
the circle, and as the only side of the machine that offers 
resistance to the centrifugal force is the outer side, it is di- 
verted from its course; but, on the other hand, the outer 
wing, describing a wider curve and traveling faster than the 
inner side, passes through more air and generates a greater 
pressure, with the result that the wing rises and tends to 
check the skidding tendency. This rising movement, though, 
must be regulated by the manipulation of the ailerons or the 
warping of the wings: by depressing one aileron and raising 
the other or warping the wings in an opposite sense for an 
amount proportional to the centrifugal force, the machine 
is made to take the curve with a lean to one side, just enough 



THEORY OF FLIGHT 21 

to allow it to bank itself properly and counterbalance the 
effect of the new force caused by the turning motion. 

The tilting of the aeroplane, and consequently of the air 
resistance, brings about a decrease in the lift and, therefore, 
the aeroplane will sag. The aviator must figure on this 
sagging motion before he starts to turn, to be sure to clear 
anything that might be below the machine. 

This falling motion can not, of course, be avoided by in- 
creasing the speed, because both centrifugal force and air 
resistance are proportional to the square of the velocity; 
consequently, the higher the speed, the greater the centrif- 
ugal force and the bigger the degree of tilting necessary to 
overcome it, and, obviously, the greater the fall. 

Having seen the effect of the new force on a machine in 
general, let us consider, now, the behavior of a machine 
having the center of gravity in a different position. There 
can be only three cases: center of gravity on a level with, 
above or below the center of pressure. 

In the case of the center of gravity on a level with the 
center of pressure, if the machine is tilted just right, it will 
follow its right course without skidding; but if it is tilted 
too far, it will slide toward the center of the circle; 
and if tilted too little, it will skid to the outer side of the 
curve. 

If the center of gravity is above the center of pressure, 
the turning movement is facilitated, because, in tilting the 
machine, the center of gravity, being high, will tend to cause 
the machine to fall, so to say, toward the center of the circle; 
but this tendency, being counterbalanced by the centrifugal 
force, will make the machine go perfectly around without 
skidding. With this position of the center of gravity, turning 
movements can be accomplished at a very high speed and, 
therefore, this is the best system for circling around. 

When the center of gravity is below the center of pressure, 
on account of the tilting and the consequent decrease in 
lift, the center of gravity tends to restore the equilibrium 



22 AVIATION 

of the machine, and to bring the wings to a horizontal posi- 
tion again, which, of course, is against the turning motion 
requirement, and the machine tends to skid. 

The conclusion to be derived from our analysis is that 
the best position of the center of gravity for straight hori- 
zontal flight is below the center of pressure, while the best 
position for turning is above the center of pressure, but as 
the latter is the worst of all to maintain equilibrium in straight 
flight, we can say that the best position of the center of grav- 
ity is below the center of pressure. 

An aeronautical engineer, while admitting that for the 
present this is the best way, expresses the opinion that the 
future will see the center of gravity above the wings, because 
by that time the aeroplane will have acquired such a great 
rate of speed as to render it indifferent to atmospheric 
currents. But, considering the ever present menace of 
hurricanes, it is very doubtful that this will be the case, 
because, even admitting what he says in regard to speed, 
it is always possible that a slackening in the power of the 
motor, if not its complete stoppage, will cause it to diminish 
and then the aeroplane will be left at the mercy of the wind, 
which may force it to pay an unpleasant visit to Mother 
Earth. 

Directional Stability. — As in the case of the longitudinal 
stability, the directional stability is obtained and controlled 
by means of additional stationary and movable planes. At 
the tail end of the machine, there are a stationary vertical 
stabilizer and a rudder. If the machine side slips or a gust 
of wind strikes it sideways, the pressure of the air will act 
on the vertical stabilizer, the tail will swing around, cause 
the nose of the machine to turn toward the direction of the 
side slip or wind and right its course. 

The rudder, instead, is moved at the will of the aviator 
and caused to turn to the right or left, thus bringing about 
a corresponding motion in the machine and changing its 
direction. 



THEORY OF FLIGHT 23 

Inherent Stability. — Analyzing the three different stabili- 
ties, we see that, aside from the balancing of the four forces 
acting on an aeroplane, they are obtained by means of 
additional planes, some of which are fixed and act automati- 
cally, and some others are movable and controlled by the 
aviator. This means that, without the controlling hand of 
a skilled and alert pilot, the machine would lose its balance 
at the first adverse condition. While, of course, it is possible 
to handle a machine of this kind, on the other hand, its 
operation is very tiresome to the operator, who can not fly 
for more than a few hours before he needs a rest, and this 
besides the fact that the controls operate only as long as 
the machine has forward speed, failing which, the aviator 
can not use them effectively. What we need, therefore, 
is a machine which acts automatically, approaching as much 
as possible the neutral equilibrium, and such an inherently 
stable machine is in existence to-day. Provided there is 
enough distance between a machine of this kind and the 
ground, to allow the righting forces to become operative, 
the machine can be thrown into any position, even upside 
down, and it will resume automatically its normal flying 
position. It is even possible for the aviator to fold his arms 
and allow the machine to fly itself. The only requirement 
in these cases is that the machine be at a fair altitude; so 
that we can assert, contrary to the popular belief, that in 
height there is safety. The disadvantages of an inherently 
stable machine are a slight loss of lift and sensitiveness of 
control, but they, of course, will never outweigh the all 
important factor of safety first, and after all, in this, as in 
any other case, a compromise is effected, by which the ma- 
chine is built with a fair degree of both inherent stability 
and manual control. 

Inherent stability in an aeroplane is attained by placing 
at angles its different planes, and these angles are : the longi- 
tudinal dihedral angle for inherent longitudinal stability; 
the lateral dihedral angle for inherent lateral stability and 



24 



AVIATION 




CL 




the angle of sweepback for both inherent directional and 
longitudinal stability. 

Longitudinal Dihedral Angle. — The longitudinal dihedral 
anjrle is the angle a (Fig. 13a) formed by the prolongation 

of the chord of a wing 
with that of the hori- 
zontal stabilizer of a 
machine, and it is made 
possible only by the de- 
calage or difference in 
the angle of incidence 
between the wings and 
the horizontal stabilizer. 
The longitudinal dihe- 
dral angle is given to an 
aeroplane to maintain in- 
herent longitudinal sta- 
bility. 

Suppose that, while 
flying at its normal 
angle, the machine sud- 
denly dives and assumes 
a tail-high position (Fig. 
136). In this case, as 
the momentum keeps 
the machine moving forward, the resistance of the air acts 
on the upper side of the horizontal stabilizer and sends the 
tail down, bringing the machine back to its normal posi- 
tion. If, instead, the tail drops (Fig. 13c), the case is re- 
versed; that is, the air strikes the under side of the hori- 
zontal stabilizer and sends the tail up again. 

The sensitiveness of the tail in restoring the longitudinal 
stability depends on the kind of horizontal stabilizer used, 
which makes the tail lifting, semilifting or non-lifting. 

A lifting tail has for a horizontal stabilizer a lifting plane, 
with the usual upper convex camber and lower concave 




THEORY OF FLIGHT 25 

camber (Fig. 14a), set at an angle of incidence smaller than 
that of the wings. While this has the advantage of lifting 
part of the weight of the machine, it has the disadvantage 
of not being sensitive in restoring the longitudinal stability, 
because when the angle of attack 
of an aeroplane changes and brings 
about a corresponding change in 
the angle of the horizontal sta- 
bilizer, although the latter gains or 
loses more incidence in proportion, 
being set at a smaller angle than 
the wings, it still retains an angle 
of incidence, and, consequently, 
has lift, which militates against 
sensitiveness. In other words, if 
the angle of incidence of the wings q 

is 3° and that of the horizontal F - 14 

stabilizer 2°, and the aeroplane 

dives until the angle of attack of the wings becomes 2°, the 
angle of the horizontal stabilizer becomes 1°; in this way, 
the wings have lost 1 / 3 of the angle, while the horizontal 
stabilizer has lost 1 \i, and the consequence is that the tail, 
having no more enough lift to carry its own weight, falls. 
If the case is reversed, that is, if the tail drops until the 
angle becomes 3°, that of the wings becomes 4°; in this case, 
the horizontal stabilizer has gained 1 /z of its angle, while 
the wings have gained 1 / 3 , and, consequently, the tail, having 
more lift than normally needed, rises. 

A semilifting tail has a horizontal stabilizer with a slight 
upper camber alone, the lower side being flat (Fig. 146), 
set at a zero angle of incidence. As the lift is just enough 
to carry the weight of the tail and the angle is zero, the 
slightest diving motion of the machine or dropping of the 
tail, setting the horizontal stabilizer at a negative or posi- 
tive angle, produces a quick righting force, which restores 
the longitudinal stability. This arrangement constitutes a 



26 



AVIATION 



happy medium of lift and sensitiveness and ' is in general 
use. 

The non-lifting tail has a horizontal stabilizer with a 
convex camber on both sides (Fig. 14c), set at a zero angle 
of incidence. As the lift of one side neutralizes that of the 
other, being equal and opposite, and the angle is zero, this 
kind of horizontal stabilizer renders the tail the most sensi- 
tive of all, but the wings must carry the entire weight of the 
machine and its center of gravity must be far forward to 
balance the weight of the tail. 



-<r-S* 




Fig. 15 



Lateral Dihedral Angle. — The lateral dihedral angle is 
the angle a (Fig. 15a) formed by two wings when they are 
tipped upward and it is given to an aeroplane to obtain 
inherent lateral stability. 

If a gust of wind strikes the machine sideways and sends 
one wing up and consequently the other down (Fig. 156), 
the center of gravity G of the machine, being displaced, G', 
tends to regain its normal position and to bring the machine 
back to an even keel. In the meantime, the wing that is up 



THEORY OF FLIGHT 



27 



loses some of its lift, due to a smaller horizontal equivalent 
A B than before A C, and tends to drop, while the lower 
wing, having more lift caused by a greater horizontal equiv- 
alent A D than before A E, resists the dropping effect of the 
higher wing. The outcome is that the higher wing, being 
compelled to fall on ac- 
count of both the dis- 4. 
placement of the center 
of gravity and the di- 
minution of lift, and 
being in the meantime 
resisted by the lower 
wing, side slips toward 
the direction of the 
lower wing. This side 
motion brings a press- 
ure against the vertical 
stabilizer A (Fig. 15c), 
which causes the nose 
of the machine to swing 
around toward the di- 
rection of the slide; the 
higher wing, being on 
the outside of the 
curve, acquires more speed and climbs again, to fall back 
again and repeat the same oscillating motion, with a con- 
tinuously diminishing intensity, until the equilibrium is 
finally restored. 

The swinging motion of the machine is detrimental, but 
unavoidable, as is also the diminution of lift, due to the in- 
clination of the wings, which have a smaller horizontal equiv- 
alent than they would have if they had no angle, but con- 
sidering the benefit derived, it is better to have a lateral 
dihedral angle, even if some lift is lost. 

The greater the angle, the greater would be the inherent 
lateral stability, but the smaller the lift, so that a compro- 




28 AVIATION 

mise is attained by setting the wings at a small angle, which 
combines a fair degree of stability and lift. 

Angle of Sweepback. — The angle of sweepback is the 
angle a (Fig. 16a) formed by the leading edge of a wing 
with the lateral axis A B of an aeroplane. It gives both in- 
herent directional and longitudinal stability to a machine. 

If the aeroplane is diverted from its straight course, one 
of its wings A (Fig. 166) assumes a more inclined position 
than the other B, and the air, offering a greater resistance 
against the wing B, which presents an equivalent surface 
C D greater than that D' E of the other A, forces the more 
exposed wing B back and restores the directional stability. 

If the machine dives, the air resistance acts on the upper 
sides F and G of the wing tips and forces up the nose; if, 
instead, the tail drops, the air acts on the under side of the 
wing tips and forces up the tail, thus restoring the longitu- 
dinal stability. 

As the directional stability of a machine does not present 
much difficulty, besides the fact that the vertical stabilizer 
promotes it, and the longitudinal stability can be maintained 
by means of the longitudinal dihedral angle with less loss 
of lift than the sweepback entails, and also on account of 
difficulty of construction, the sweepback is not much used. 

Vertical Stabilizer. — The inherent directional stability is 
maintained in almost all aeroplanes by means of the vertical 
stabilizer, which is a flat triangular plane bolted on the upper 
part of the tail. 

If during flight a gust of wind strikes an aeroplane on 
one side A (Fig. 17a), the pressure, although acting on the 
entire aeroplane, produces more effect on the vertical stabili- 
zer B on account of its long lever arm and causes it to swing 
to the opposite side C (Fig. 176). As momentum tends to 
keep the aeroplane in its previous direction, the pressure of 
the air acts now on the other side of the vertical stabilizer 
and forces it back to its former position, thus righting the 
course of the aeroplane. 



THEORY OF FLIGHT 



29 



If the case is reversed, the same principle holds good. 
Gliding Angle. — One of the most important points to 
consider, in connection with the inherent stability of an 



CL 




Fig. 17 

aeroplane, is that when the motor is stopped and gravity 
furnishes the motive power. 

It is clear that in this case the machine can do nothing 
but glide down, and to do so safely, it is imperative that it 
assume the proper gliding angle automatically. To this 
end, the four forces which act on an aeroplane are disposed 
so that the center of gravity G (Fig. 18) is a little in advance 
of the center of lift L, and the center of resistance R a little 
above the center of thrust T. Due to the disposition of the 
center of gravity ahead of the center of lift, the aeroplane 
would come down nose foremost, if no other force counter- 



30 



AVIATION 



acted that of gravity; but when the motor is working, this 
opposing force is furnished by the thrust of the propeller, 




Fig. 18 

and when it is stopped, the necessary force is supplied by 
the pressure of the air against the center of resistance, which, 
being above that of the thrust and far in advance of the 
center of gravity, resists the nose-diving tendency of the 
aeroplane to such an extent as to make it assume the proper 
gliding angle automatically. 

The location of the point of application of each force, which 
determines the degree of the gliding angle ABC (Fig. 19) 
A of an aeroplane, determines 

also, as a consequence, its 
radius of action C B or hori- 
zontal equivalent of the 
gliding path A B. 



£1 



"r~ — - B 



Fig. 19 



The radius of glide is altered by the power of the wind, 
being increased or decreased according to the direction of 
the aeroplane in relation to that of the wind. 

The gliding angle is usually expressed in terms of the 
ratio of the height of glide A C to the radius of glide C B; 



THEORY OF FLIGHT 



31 



that is, if the height from which an aeroplane starts to glide 
is 1 mile and the distance traveled in a straight horizonal line 
in reference to the ground is 6 miles, it is said that the gliding 
angle is 1 in 6. 

As the radius of glide is directly proportional to the height 
of glide, we have here again the confirmation of the fact 
that height means safety, because it gives a greater radius 
of action and, therefore, affords the pilot a better opportu- 
nity to choose a suitable landing place. 

Propeller Torque. — Among the different causes which 
affect the lateral stability of an aeroplane, one deserves 
special consideration: the 

propeller torque. This ro- & ^r^v * A 

tary force tends to produce 
an opposite rotary motion 
to the point of application, 
which, if free to move, will 
actually revolve, as is the 
case with the helicopter us- 
ing only one propeller. If 
the propellers are two or 
any even number, the effect 
of the torque is eliminated 
by making one-half of them 
revolve in the opposite di- 
rection to the other half.' 

In the case of a machine having one propeller, the result 
is that one wing A (Fig. 20a) is forced down, and, conse- 
quently, the other one, B, up. To correct this direct effect 
of the propeller torque, the angle of incidence near the tip 
of the lower wing is increased or washed in to a degree neces- 
sary to give it enough additional lift to bring the wing back 
to its normal position and restore the lateral stability. The 
same correction can be made by decreasing or washing out 
the angle near the tip of the high wing B (Fig. 20b) to bring 
it down to its proper level. A better system, though, is to 




Fig. 20 



32 AVIATION 

increase the angle on one side A (Fig. 20c) and decrease it 
on the other B by one-half the amount needed for the total 
increase or decrease. One reason why this method is to be 
preferred is that an increase in lift means also an increase in 
drift, which causes the wing with the bigger angle to retard 
its forward motion and to bring about a consequent turning 
movement in the machine, which will be greater, the greater 
the drift, and this, of course, is the case when the angle is 
increased or decreased all on one side. Another reason is 
that when the ailerons are used to restore the lateral stability 
by bringing one up and the other down, they do not work 
in air with the same density, because the lower aileron re- 
ceives the compressed air from the lower camber, while the 
upper receives the rarefied air from the upper camber, and 
the consequence is that the lower aileron is more effective 
and introduces in the meantime more drift than the upper, 
with the result that the machine swings around towards the 
side of the lower aileron, and this makes necessary the opera- 
tion of the rudder in conjunction with the ailerons to keep 
the straight course of the machine. The smaller the angle 
near the wing tips, the smaller the drift of the lower aileron, 
the smaller the turning tendency of the machine and the 
smaller the angle of the rudder. By dividing the angle 
equally between the wing tips, therefore, the amount of 
drift is reduced to the minimum and so the consequent 
turning motion, both in regard to that caused by the correc- 
tion of the direct effect of the propeller torque and the other 
brought about by the manipulation of the ailerons. 

To correct the indirect effect of the propeller torque, 
either the rudder or the vertical stabilizer is set at an angle 
toward the wing tip which has less incidence, thus introducing 
an equal amount of drift to that side of the machine and 
restoring the directional stability. As the torque of the 
propeller varies with the power of the motor, being com- 
pletely absent when the motor is stopped, and is not there- 
fore a fixed quantity, while the angle at the wing tip is, it 



THEORY OF FLIGHT 33 

becomes necessarj' to correct by manipulation the varia- 
tions in the stability of the machine, produced by the change 
in the torque. For this reason, it is better to use the rudder 
in correcting the indirect effect of the propeller torque, 
because the rudder can always be moved at will by the 
aviator, while the vertical stabilizer is bolted in place and 
once set, is set to stay. 



CHAPTER II 
AEROPLANE CONSTRUCTION 

Parts 

The main parts of a monoplane are four; those of a bi- 
plane may be four or five. We will consider the case of the 
biplane with five parts, which, when named in their assem- 
bling order, are the following: fuselage, undercarriage, center 
section, wings and empennage. 

All these parts are light and strong structures produced 
by a skillful combination of wood, metal and fabric. 

Fuselage. — The fuselage (Fig. 21) is the main body of the 
aeroplane, all other parts being attached to it. 

The wooden parts of the fuselage are: the longerons, top A 
(Fig. 21a) and bottom B (Fig. 216) ; the struts, top C (Fig. 
21a), bottom D (Fig. 216) and side E (Fig. 21c); the tail post 
F (Fig. 21c) and the engine rails G (Fig. 21a). The metallic 
parts are: the fittings H (Fig. 21c) with their rivets or clevis 
pins and cotter pins or bolts, nuts and cotter pins; the turn- 
buckles M (Fig. 21a) ; the cross bracing wires, top / (Fig. 21a), 
bottom J (Fig. 216), side K (Fig. 21c) and internal L (Fig. 
21d); the nose plate N (Fig. 21a); the engine rails support 
(Fig. 21a); and the reenforcing struts P and Q (Fig. 21c). 

At the tail end of the fuselage is the rudder post R (Fig. 
21c) and on the under side is the tail skid S (Fig. 21c), which 
sometimes is attached to the rudder post and sometimes 
to an independent piece T (Fig. 21c). 

The longerons are made of strong wood, as they must 
stand all kinds of stresses without breaking, because to 
change a damaged longeron means to dismantle the fuselage 
and, consequently, the entire machine. 
34 



AEROPLANE CONSTRUCTION 



35 



The struts are lighter and weaker wood, intended to take 
only a compression stress. 

The tail post is not used in all machines, as sometimes 
the rudder post has the double function of tail post and 
rudder post. 





Fig. 21 

The engine rails are very strong wood, usually laminated, 
and they are fixed in place in the strongest possible way, 
because on them is bolted the motor. 

The fittings are metallic fixtures which connect the joints 
of the struts and longerons. The wires are also attached 



36 AVIATION 

to them by means of rivets, pins or bolts. The fittings and 
their fixtures are used in all the other parts of the machine 
and they will be omitted hereafter, unless meant for a special 
purpose. 

The turnbuckles are couplings, with a barrel and a right 
and a left hand eye screw or shank, used to regulate the 
length and tension of wires. The right hand screw shank, 
which sometimes is split or forked, is generally attached 
to a fitting. This is done to determine the turning direction 
of the barrel in tightening or loosening a wire, as, in this 
case, the operation is that of an ordinary right hand screw 
nut. The come and go is the distance the shanks can be 
screwed in or out. The turnbuckles also are used for all the 
wires and they will be omitted in the descriptions of the 
other parts of the machine. 

The cross bracing wires are of the greatest importance, 
as from them depends the rigidity and consequent strength 
of the entire machine. 

The nose plate, engine rails support and the reenforcing 
struts are used to give the strength and rigidity required 
for the installations of the motor, whose vibrations might 
cause the loosening of some weak part and cause a disaster. 

The rudder post is a metallic tube to which is hinged the 
rudder. 

The tail skid is a strong piece of wood and is attached under 
the tail of a machine to carry the weight of its rear portion 
while on the ground and to act as a shock absorber and brake 
in landing. It is better to have the tail skid attached to an 
independent piece, rather than to the rudder post, because 
in case of a bad landing, the latter may be distorted so as to 
jam the rudder. 

The main sections of the fuselage are : the engine section A 
(Fig. 22), the cockpit B and the tail section C. 

The fuselage is covered all around with cowling or fairing 
to give it a stream-lined shape. This cowling is metal for 
the entire engine section and the upper part of the cockpit, 



AEROPLANE CONSTRUCTION 



37 



the balance being fabric, sometimes reenforced by a light 
framework of wood, and this is especially the case with the 
part that covers the tail section. The cowling of the top 
takes special names, according to the section it covers: hood 




D for the engine section, cowl E for the cockpit and turtle- 
back F for the tail section. 

The fuselage is constructed in the strongest possible man- 
ner to withstand all kinds of stresses, and as the other main 
parts are attached to it, its fittings are so made that while 
they hold its own members together, they are ready to re- 
ceive the other parts of the machine. 

The fuselage is usually made in a square section, built 
box girder fashion and has a fineness of 7. Although stream- 
lined to diminish the passive drift as much as possible, this 
shape does not represent the last word in science, it being 




Fig. 23 

well known that other experimental models have given much 
better results. The future will undoubtedly see the shape 
of the fuselage so altered as to give the least amount of drift. 
There is a cigar-shaped fuselage (Fig, 23) specially con- 
structed and covered all around with plywood, so as to form 
one single shell and for this reason is called monocoque, 
which in French means one shell. 



38 



AVIATION 



Sometimes the common box girder type of fuselage is 
covered also with plywood, monocoque fashion. 
There is another kind of short body or cut off fuselage 
called nacelle (Fig. 24), which is 
used for machines that have the 
propeller in the rear. 
r""" " — li^l Undercarriage. — The undercar- 

\ f d riage (Fig. 25) is that part of the 

\. ^^^ ' machine designed to support it 

when at rest, to absorb the shock 
of landing and to give clearance to 
the propeller and wings. 
The wooden parts of the undercarriage are: the struts A 
(Fig. 25a) and the spreader B; the metallic parts: the cross 
bracing wires C, the axle D, the wheels E, the shock absorber 
fittings F (Fig. 256) and the radius rods G. 

Besides these, there are additional parts of rubber, that 
is, the tires for the wheels and the cables of rubber used as 
shock absorbers. 

The struts of the undercarriage are made purposely weaker 




Fig. 24 





Fig. 25 



than the longerons of the fuselage, so that in case of a hard 
landing, it will be the struts which will break, as they are 
easily replaced. 



AEROPLANE CONSTRUCTION 39 

The spreader keeps the struts at the proper distance and 
is stream-lined to diminish the drift. 

The wheels used for the undercarriage are the same as 
those for automobiles and they run up to 32 inches in di- 
ameter. The heavier the machine, the larger the wheels, 
but the standard size is 26 x 4, that is, a wheel of 26 inches 
and a tire of 4 inches diameter. The larger the diameter of 
the wheels and tires, the better suited to run on rough ground, 
but of course the weight compels the limitation of the size. 
The hubs of the wheels have no ball or roller bearings to 
be lighter, but the spokes are very substantial and well 
spread out to resist side stresses. 

The tires are of the double tube type, that is, they have 
an air casing and a shoe or outer casing. The center of the 
shoe is harder, because it is the part that comes in direct 
contact with the ground and is called the thread. The press- 
ure that a tire can stand is 20 pounds per sectional linear 
inch, but this pressure is never given, because the tire, besides 
being used to facilitate the run on the ground, must absorb 
some of the shock of landing. The spokes of the wheels 
are covered on both sides with disks of metal, canvas or cel- 
luloid to stream-line them, and in this case they are called 
disk wheels. 

The shock absorbers used to-day. are generally of rubber, 
in the form of a cable of strands of rubber covered with 
fabric, wound around the undercarriage fittings and the 
shock absorber fittings. It is important that the cables of 
both wheels have the same tension, to prevent a side motion 
of the machine in moving along the ground and particularly 
in landing, when it would be very dangerous and might 
cause the machine to turn over sideways. The strands of 
rubber run from 50 to 300 and the size of the cable from half 
an inch to one inch. The length of cable used is proportional 
to its diameter and the weight of the machine. These shock 
absorbers are preferred because they are readily adjusted and 
replaced, their deterioration is easily detected and they ab- 



40 AVIATION 

sorb much more than steel per unit weight. They are not 
ideal, though, because the more they stretch, the less they ab- 
sorb, and a shock absorber should really absorb the shock of 
landing without giving a rebound. This could be obtained 
by the use of the hydraulic or oleo pneumatic shock absorbers. 
They consist of two tubes, one inside the other, separated 
by either water or oil; the outer tube is attached to the axle 
of the wheels and the inner tube to the undercarriage. When 
the machine is in flight, the weight of the wheels and axle 
pulls the outer cylinder down and the liquid flows all in 
the outer tube. When the machine lands, the inner tube 
presses the liquid and forces it inside of the inner tube through 
a valve at its bottom, and as it goes in, the air in the inner 
cylinder resists it, thus forming a cushion of air which ab- 
sorbs the shock, while the liquid, through ports in the inner 
cylinder, is forced out and back again into the outer tube. 
As, after landing, the shock-absorbing power does not exist 
any more, and it is necessary to have some of it when the 
machine is pulled about on the ground, an additional spiral 
spring is provided, which comes into play when the inner 
cylinder reaches the limit of its downward run. The liquid 
is generally oil, because it is less liable to freeze than water. 
Although these are real shock absorbers, they are not used 
much on account of their weight, complication of parts and 
high cost. 

A kind of shock absorber, w T hich is a combination of shock 
absorber and wheel, is the Ackerman wheel, whose spokes are 
S shaped for the purpose of absorbing the shock of landing. 

An important point to be observed in regard to the use 
of the rubber shock absorbers and the Ackerman wheel 
is that in the first case the rubber cable is wound around 
the undercarriage fittings and the shock-absorber fittings, 
which means that when the machine lands, the axle must 
give and stretch the rubber; while the axle of the Ackerman 
wheels must be rigidly attached to the undercarriage, as 
in this case it is the spokes that absorb the shock. 



AEROPLANE CONSTRUCTION' 41 

The radius rods are guides pivoted to the axle and the 
struts, to prevent the possibility of the axle striking and 
breaking the struts when the machine lands and the wheels 
and axle jump up. 

Some machines have neither radius rods nor separate 
shock-absorber fittings, in which case there is a special axle 
fitting, which is a combination of all these parts in one. 

The undercarriage deserves a good amount of thought to 
avoid damage both to the aviator and the machine even 
before they leave the ground. The weight of the machine 
rests on the undercarriage, therefore it must be strong enough 
to withstand the stress of its load when at rest, more so when 
moving, because of the increased stress imposed by the 
shocks imparted by the runs on an uneven ground, and in 
the greatest degree when landing. 

The undercarriage should be so built as to give a quick 
start and a quick stop. Evidently these are opposite re- 
quirements, because if a machine must start quickly, it 
means that the wheels must give the least amount of friction 
and, for this very reason, the machine can not stop quickly. 
To accomplish both results, it is necessary to have a brake, 
which will stop the machine at the proper time in landing. 
This mechanical brake would be a very good addition to an 
undercarriage, because often it happens that a machine lands 
on slanting ground and the aviator has no means of stopping 
it to avoid a smashup; but, on the other hand, the brake 
requires a proper adjustment to avoid the tendency of the 
machine to come down on its nose when the brake is applied. 

The undercarriage should be well sprung and strong enough 
to withstand rolling and side shocks without deflection or 
fracture, and it should also offer the lowest drift when in 
flight, which means that all its parts must be stream-lined 
and so disposed as to take full advantage of the shielding 
effect. 

The height of the undercarriage depends upon the diameter 
of the propeller, which should have a clearance of from one 



42 AVIATION 

to two feet to prevent breakage due to the tilting of the 
machine or to the sinking of the wheels into soft ground. 

The center of gravity of the machine is usually very near 
the center of the wheels, and therefore the tail section of the 
fuselage and the skid are built lightly. If the center of grav- 
ity is too far back, it is necessary to have a heavy fuselage 
and skid, which, in landing, cause a heavy drop of the tail 
and a consequent increase of the angle of incidence of the 
wings, and the result is that the machine rebounds. A heavy 
fuselage means greater frictional resistance for the skid, which 
prevents a rapid start. 

If the machine has a lifting tail, the tail end of the fuselage 
and the tail skid can be built much lighter than when the 
tail is non-lifting. 

Center Section. — The center section (Fig. 26) is the central 

structure which con- 

A 



f — *■" — — ts ^3 The principal part 



nects the upper wings 
« p ^ a^ . of a multiplane. 



of the center section is 
i the panel A, which is 

-p. 26 a section of wing and 

the part always missing 
in a monoplane and sometimes in a biplane. The reason is 
this: the monoplane has only one set of wings and they are 
fixed directly to the fuselage; the biplane, instead, being pro- 
vided with two sets of wings, has the lower ones attached to 
the fuselage as in a monoplane, while the upper wings are at- 
tached to the center section, in which case the main parts 
will be five ; or they are united end to end by means of fittings 
and supported by struts, and then there is no center section, 
in which case the parts of a biplane are also four as in a 
monoplane. 

The wooden parts of the center section are the struts B, 
and the metallic parts: the cross bracing wires C, the bracing 
wires D (Fig. 266), the drift wires E and the antidrift wires F. 



AEROPLANE CONSTRUCTION 



43 



The cross bracing wires of the center section are found 
usually in the front and the rear, the bracing wires taking 
the place of the cross bracing wires, which should be on the 
sides also. These side cross bracing wires are eliminated and 
substituted by the bracing wires, because the seat of the 
aviator is almost always inside of the center section and, 
consequently, the sides must be free from obstructions, so 
that he can go in and out. 

The drift wires have the object of strengthening the center 
section against the pressure of the air when the machine is 



£1 



n 



\ 



„ A 



i^ 



A 



v 



A? 



G? 



L^\A 



N 



c . 




Fig. 27 



in flight, and the antidrift wires are necessary to counteract 
the tension of the drift wires and to keep the center section 
straight and rigid. 

Wings. — The wings (Fig. 27) are the lifting members of 
the machine, whose entire weight hangs from them, and 
therefore they must be built very strongly. 

The wooden parts of the wings are : the spars, front A and 
rear B; the compression ribs C, the camber ribs D and the 
false ribs E; the leading edge F and the trailing edge G; 
the wing tip H; the stringers / and the three-ply veneer J. 
The metallic parts are : the drift wires K, the antidrift wires 
L and the hinges or Sittings M. 



44 AVIATION 

The wings are covered with fabric, which is made tight by 
coating it with a special solution. 

The compression ribs are solid and are used for strength, 
while the camber ribs are lightly built and their purpose is 
to give the proper shape to the fabric. The false ribs are 
merely strips of wood, which run from the leading edge to 
the front spar and they are used to prevent the fabric from 
sinking between the ribs proper. Sometimes, instead of the 
false ribs, the three-ply veneer is used, and sometimes, both 
false ribs and three-ply are found in the same wing. 

A rib is made of three parts: a web A (Fig. 28) and two 
cap strips B and C. The web or center part is made in three 
pieces, leaving two openings for the spars. 




Fig. 28 

The stringers are long strips of wood running through the 
webs of the ribs to keep them from rolling over. Sometimes, 
these pieces are round and they are called dowels. 

Generally, a wing is cut toward the rear edge so as to form 
a rectangular plane N, which constitutes a part by itself and 
is hinged to the wing; this is the aileron. Sometimes, the 
part where the aileron should be is not cut off, but is made 
flexible, so that it can be warped up or down, and this is 
especially the case with the monoplane. 

The ailerons are used to control the lateral stability of a 
machine and to bank it properly during a turn. 

Empennage. — The empennage (Fig. 29) is the tail of the 
machine. 

The parts of the empennage are: the horizontal stabilizer A, 
the vertical stabilizer B, the elevators C and the rudder D. 



AEROPLANE CONSTRUCTION 



45 



All these parts are constructed in the same way as the 
wings, that is, they consist of a framework of wood, braced 
by wires and covered with coated fabric. 




Fig. 29 

The horizontal stabilizer maintains inherent longitudinal 
stability and the vertical stabilizer inherent directional 
stability. 

The elevators are used to make a machine climb or descend 
and the rudder to make it turn to the right or left. 

Wires. — When the wings of an aeroplane are mounted, 
they are held rigidly in place by means of additional wires, 
struts and metallic tubing. 

In a monoplane, these additional bracings are: the cabane 
A (Fig. 30a), which is a metallic framework built on the 
upper part of the fuselage; the landing wires B, which run 
from the top of the cabane to the upper part of the wings 
and hold them when the machine is on land; the flying wires 
C, which run from the undercarriage to the lower part of the 
wings and hold them when the machine is in flight; and the 



46 



AVIATION 



drift wires D (Fig. 306), which run from the nose plate to 
the wings and hold them against the drift during flight. 

The cabane is a necessity in a monoplane, because if the 
landing wires were attached directly to the fuselage, they 




Fig. 30 

would be too low and would hardly have any bracing strength. 
Even attached as they are, these wires, and also the flying 
wires, do not give much strength to the wings, running to 
them at a slant, and, consequently, the monoplane is weak 
in construction, although very efficient in regard to lift. 
In a biplane or multiplane, the additional bracings are: 



AEROPLANE CONSTRUCTION 



47 



the interplane struts A (Fig. 31a), which hold the wings 
apart; the landing wires B; the flying wires C; the stagger 
and incidence wires D (Fig. 316), which brace the wings one 





Fig. 31 

with the other; and the drift wires E, which run from the 
nose plate to the wings. 

Such a box girder bracing makes the biplane very strong 
in construction, but it detracts from its lift, increasing the 
passive drift and causing interference in the gap. For parity 
of surface, the lift of the biplane is about 85 per cent that 
of the monoplane. 

When a biplane has an extension, further bracings are used 
to strengthen it. These are: the king-post F (Fig. 31a), the 
bracing wires G, which serve as landing wires, and the flying 
wires H. 

The landing wires usually are single, being sufficient to 



48 AVIATION 

carry the weight of the wings when the machine is on the 
ground and to stand the additional stresses of normal and 
abnormal landings. The flying wires, instead, are double, 
because they must carry the entire weight of the machine 
and stand all the abnormal stresses imposed by the different 
positions assumed by it in flight. The important fact must 
not be overlooked, however, that sometimes the landing wires 
are subjected to the abnormal stresses produced by a re- 
versal of loading, which equal, if indeed they do not surpass, 
those of the flying wires. This takes place in such cases as 
steep gliding, upside down flying and rolling, when the 
weight of the machine is borne in part or in full by the top 
of the wings and transmitted to the landing wires. For these 
performances, a machine must have double landing wires. 
Power Plant. — A very important part entering in the 
a construction of an 

aeroplane is the 
power plant, which 
to-day is the four- 
stroke gasoline mo- 
tor, being the light - 
z est and most pow- 

^ erful invented so 

far, although it has 
the great inconveniences of high speed, vibrations and 
noise. 

The position and number of motors give different names 
to an aeroplane: if the motor is in front, the aeroplane is a 
tractor; if in the rear, a pusher; and if the motors are two, 
a twin-motor aeroplane, either tractor or pusher. 

The tractor aeroplane (Fig. 32) has the disadvantage of a 
limited range of vision A B, because, on account of the motor 
in front, the aviator has to sit in the rear part of the machine 
to balance it, and the wings limit his visual radius; but, on 
the other hand, it is less dangerous for the aviator in case of 
a fall, because the motor is in front and can not drop on him. 




AEROPLANE CONSTRUCTION 



49 



The pusher (Fig. 33) has an unlimited range of vision, 
because the aviator sits in the front part of the machine, 
but in case of a fall, the motor may drop on him and crush 
him to death. Another great disadvantage of the pusher 
aeroplane is that it 
needs outriggers A to Y 

give clearance to the 
propeller. The out- 
riggers increase the 
weight and drift, due 
to their size, position 
and necessary bracing 
with struts and wires. 
It was just on account 
of this awkward con- g " 

struction that the propeller was tried in front, although all 
authorities agreed that for efficiency its best position was 
in the rear, but when the first trial was made, a most as- 
tounding result was obtained: the lift was more than doubled. 
This is due to the fact that the relative speed of the air is 
increased by being thrown back by the propeller against 
the machine. It is true that the passive drift is increased, 
also, and more power is needed to overcome it, but on the 
other hand, the surface of the wings can be cut down, making 
it possible to shorten the span and increase the strength 
of the wings, which is a very great advantage, especially 
in the case of a monoplane. 




Controls 

The controls are mechanical devices used to operate the 
controlling planes, that is, the ailerons, the elevators and 
the rudder. 

The controls in use to-day are two: the wheel control, called 
also Deperdussin or Dep, and the stick control. In both 
mechanisms, the hands are used to operate the ailerons and 



50 



AVIATION 



elevators, which require finer motions, and the feet for 

operating the rudder. 

The wheel control (Fig. 34) consists of a hand wheel A 

(Fig. 34a), a drum B, a control column C, two pulleys D 

and a wire E. The 
wheel is pivoted to 
the upper end of the 
control column and 
is free to turn to the 
right and left, while 
the other end F of 
the control column is 
pivoted to the bot- 
tom of the cockpit 
and can be moved 
only in a fore and aft 
direction. The center 
of the wire is at- 
tached to the drum 
at one point and then 
is wound around a 
spiral groove cut in 
the side of the drum, 
so that if the wheel 
is turned to the right, 
the left end of the 
wire is pulled and t he 
right end released ; 
and vice versa. To 
the right end of this 

wire is turnbuckled a control wire G, which after passing 

around a pulley, runs to the under side of the right aileron H, 

and to the left end another wire I, which goes to the under 

side of the left aileron J. 

On the upper side of the wing with the ailerons, which 

in a biplane is usually the top wing alone, is a balance wire A', 




AEROPLANE CONSTRUCTION 51 

whose right and left end is attached to the upper side of the 
right and left aileron respectively, so that if one is lowered, 
the other one is raised, and vice versa. At the center of the 
balance wire is a turnbuckle, which is used to regulate the 
position of the ailerons in regard to the wings. All these 
wires are attached to masts, which are bolted to the control 
planes. 

With such an arrangement, a turn of the wheel to the 
right brings down the left aileron and up the right one, and 
a left turn of the wheel reverses the motions. 

On the front side of the control column is attached one 
pair of wires L (Fig. 346), above the pivot point, and on the 
rear side, opposite the first pair, is another one M . The 
front pair runs to the lower side N of the elevators, the right 
wire being attached to the right elevator and the left to the 
left; the rear pair, after passing around pulleys 0, goes to 
the top side P of the elevators and the two wires are at- 
tached similarly. The wires, therefore, cross one another, 
so that a forward motion of the wheel or control column 
pulls down the elevators, and a backward motion brings 
them up. 

The rudder Q (Fig. 34c) is controlled by a foot rudder 
bar R, pivoted in the center, and two wires, one S attached 
to the right and the other T to the left end of the bar, which 
run to the right and left side of the rudder respectively. 
Thus, a push to the right or left end of the bar pulls the rudder 
to the right or left. 

The wheel, therefore, operates the ailerons; the column, 
the elevators; and the foot rudder bar, the rudder. 

This control is in a neutral position when the wheel is so 
turned that the point of attachment of the wire on the drum 
is on the top; the control column vertical and the foot rudder 
bar at right angles with the longitudinal axis of the aeroplane. 

Holding the control in neutral position, the aviator is 
enabled to operate the controlling planes easily and, with 
tae exception of the rudder, naturally. If, for instance, the 



52 AVIATION 

left wing dips down, the aviator instinctively shifts his 
body to the right to keep his balance and, in so doing, he 
carries the motion of the wheel to the right; this brings 
down the left aileron and up the right. The resistance of 
the air, acting against the lower side of the lower aileron, 
pushes the lower wing up, while the resistance against the 
upper side of the upper aileron pushes the higher wing down, 
thus reestablishing the equilibrium. If the case is reversed, 
the same principle holds good. If the aviator wants to come 
down, he pushes the wheel down, the elevators go down, and 
the air, acting against the lower side of the elevators, pushes 
the tail up and, consequently, the nose down; when he wants 
to go up, he pulls the wheel up and the motion is reversed. 
If he wants to turn to the right or left, he pushes the foot 
rudder bar to the right or left. 

While the motion of the rudder seems natural, the right 
push of the foot corresponding to the right turn of the ma- 
chine and the left to the left, it is not, and we are not used 
to this system of conrol. If we ride a bicycle, when we push 
the right side of the handle bar, we turn to the left, and vice 
versa. The same should be with the foot rudder bar and 
it could easily be accomplished by simply crossing the wires. 
Why this is not done is probably due to the fact that the 
aviators, having mastered this awkward motion, are not 
prone to change it, fearing that, through force of habit, they 
may encounter with some accident in making an involun- 
tary inverse motion when they are in a dangerous position, 
and so they teach the same system to their pupils, continuing 
the same erroneous motions. 

The stick control (Fig. 35) consists of a vertical metallic 
tube or stick A, a horizontal tube B, two arms C and two 
bearings D. The stick is forked at one end E and is pivoted 
to the horizontal tube so as to form a universal joint, which 
makes it possible to move the stick from side to side without 
moving the horizontal tube and to turn the latter in its 
bearings when the stick is pushed forward or pulled back- 



AEROPLANE CONSTRUCTION 



53 



ward; the arms are fixed to the ends of the horizontal bar; and 
the bearings fastened to the floor of the cockpit. To the stick 
are fastened two wires, one to the right F and the other to 
the left side G, which run to the right and left aileron respec- 
tively, and to each 
arm are attached 
two wires, one at 
each end, the top 
wires H (Fig. 356) 
going to the bottom 
of the elevators and 
the bottom wires I 
running to the top 
of the elevators; 
these wires, there- 
fore, cross one an- 
other. 

With this mechan- 
ism, a side motion 
of the stick oper- 
ates the ailerons and 
a fore and aft motion 
operates the elevators, 
in the wheel control. 

While the mechanisms as described here are not used in 
all machines, the changes are only means to an end, the 
principle being always the same. 

In biplanes having ailerons in both sets of wings, the 
control wire runs along the lower wings and the motions 
from the lower to the upper ailerons are transmitted by two 
compensating wires or struts, one connecting the right and 
the other the left ailerons together. With the use of com- 
pensating struts, there is no need of balance wire, because 
a strut can be used both to pull and push, while a wire can 
only pull. 

Some machines have a dual control, the two units being 




Fig. 35 
The rudder system is the same as 



54 AVIATION 

connected by additional wires and bars in such a manner 
as to make their motions synchronous. 

The wheel control is slow in its movements and is used 
for slow speed and training machines, while the stick con- 
trol is operated quickly and is found in speedy machines 
flown by experienced aviators. The stick can be manipu- 
lated with one hand and some pilots have gone so far as to 
operate it with their knees, thus leaving both hands free, 
and as the stick is round and may slip from between the 
knees, a half round pad is attached on each side to fit the 
legs and permit a good hold on the stick. This is a very 
good improvement in war machines, enabling the pilot to 
have his hands free to operate the gun. 

Pontoons 

A special aeroplane part found only in water machines 
or hydroaeorplanes is the pontoon (Fig. 36), which is a flat 




Fig. 3G 

bottomed, air-tight, boat-like float attached to a land ma- 
chine to enable it to rest on and rise from the water, skimming 
on its surface like a hydroplane. 

A pontoon is usually built with ply-wood, alternated with 
painted canvas, glued with marine glue to a thickness of 
about one-quarter of an inch and closely screwed to a frame- 
work similar to that of a boat. 

In a pontoon, we find: the step A (Fig. 36a), the vent 
pipes B, the bulkheads C, the drain holes Z), the hand holes 



AEROPLANE CONSTRUCTION 55 

E, the reenforcing struts F, the planing fins G (Fig. 366) and 
the battens H. 

The step is a very important feature of the pontoon and 
its object is to facilitate the rise of the machine by breaking 
the hold of the water from the bottom of the pontoon. 
When the machine starts to skim, the inclined bottom of 
the forward part of the pontoon presses the water down and 
makes it acquire a downward trend, which, on account of 
the adhesion of the water to the pontoon, pulls it down. As 
the step is reached, the hold of the downward current is 
broken from the bottom and is carried to the water behind 
the step. This water, being pulled downward, causes a 
vacuum behind the step, with the result that the pontoon 
can not leave the water easily, if the formation of the vacuum 
is not prevented and this is exactly the function of the vent 
pipes. Being always open to the air, they keep it in con- 
stant contact with the water at the step and avoid the forma- 
tion of the vacuum. The diameter of these pipes when 
first used was about half an inch, while now it has reached 
two and one-half inches. 

The bulkheads divide the pontoon in compartments to 
prevent it from sinking in case of a leak, confining the in- 
coming water to one section only. 

The drain holes serve to drain out the water which may 
be found in the pontoon when the machine is beached. 
The drain holes are closed by plugs. 

The hand holes are used to bail out the water while the 
machine is floating, to sponge any remains after it has been 
drained and to ventilate the pontoon when the machine is 
on land. The hand holes normally are closed by covers. 

The reenforcing struts strengthen the pontoon against the 
shock of landing, both in a vertical and inclined direction. 

The planing fins increase the planing surface of the pon- 
toon. The minimum surface should be one square foot 
for each 500 pounds of weight, but in actuality is much more 
than that. 



56 



AVIATION 



The battens are attached to the bottom of the pontoon 
to avoid damaging it when the machine is beached. 

The manner in which the pontoon is attached to a ma- 
chine gives it a different name. Although all water machines 




are hydroaeroplanes, this term is used to designate an aero- 
plane which has an undercarriage with one or two pontoons 
attached to it (Fig. 37). A machine which has a pontoon 
in the place of a fuselage is called a flying boat (Fig. 38). 

In regard to the number of pontoons used in a hydro- 
aeroplane, it is to be noted that while two pontoons give 
a better support to the machine on the water, on the other 
hand they increase the drift when the machine is in flight, 
because for equal volume they offer more surface than one 



AEROPLANE CONSTRUCTION 



57 



pontoon. Then, too, they subject the machine to heavy 
stresses in a rough sea, because while one pontoon is on the 
crest of a wave, the other is down in the trough, and this 
see-sawing motion is dangerous. One pontoon causes no 




Fig. 38 

stresses and gives less drift, but is not so steady and re- 
quires the use of additional small floats at the wing tips and 
sometimes at the tail (Fig. 376). 

Pontoons offer a great amount of lateral or keel surface, 
which renders a water machine very sensitive to side winds 
and also causes it to skid in a turning motion. To offset 
this tendency, an extra plane or non-skid fin A (Fig. 38) is 
attached to the top of the wings, which, on account of its 
long lever arm, counterbalances the pressure against the 
side of the pontoons. 



Materials 

A successful aeroplane must be the combination of strength, 
lightness, rigidity and flexibility; but to combine all these 
opposite requirements into one single structure, in order to 
render it indifferent to all kinds of stresses, is perhaps the 
most difficult problem man ever undertook to solve, which 
calls into duty almost every known branch of industry and 
commands the employment of first class skill and material. 



58 AVIATION 

That a machine should be strong, it goes without saying, 
as it must stand the pressure of the air, the vibrations of 
the motor and the shocks in starting and landing; that it 
should be light, it is a capital requirement to accomplish 
flight ; and rigid it must be as a whole to withstand distortion, 
but up to a certain degree, when flexibility comes in to avoid 
undue stiffness of the parts, which might break if stressed 
out of proportion; and that these are sine qua non conditions 
to obtain a perfect flying machine, nothing can attest more 
than the long, painstaking work of the great American 
pioneer, Professor Langley, whose noteworthy perseverance 
only could bring the hard task to completion. 

To solve the difficult problem in the best possible way, 
the materials used to-day in constructing an aeroplane are: 
wood, metal and fabric, variously combined; although the 
all-metal machine, which has already made its appearance, 
will undoubtedly be the machine of the future. 

Before we examine in detail these materials, it is necessary 
that we know something about their strength and the terms 
used in connection with it. 

Strength of Materials. — Stress is the load to which a body 
is subjected and it is expressed in pounds per square inch. 

Stresses are simple and compound; the simple are: com- 
pression, tension and shear stress; the compound: bending 
and torsion. 

Compression is the stress which tends to crush a body. 

Tension is the stress which tends to elongate a body. 

Shear stress is the stress that tends to tear a body in such 
a manner as to cause one part to slide over the other. 

Bending is the combination of the compression and ten- 
sion stresses. 

Torsion is a combination of the compression, tension and 
sheer stresses. 

The bending stress has a special importance in aeroplane 
construction. When a body is bent, its molecules on the 
outside curvature are under tension, while in the inside they 



AEROPLANE CONSTRUCTION 59 

are under compression and in the center none of the two 
stresses is felt and there is, therefore, a neutral line. This 
enables us to hollow the parts used in aeroplanes, thus saving 
about 33 per cent in the weight of material. 

All bodies have a limit beyond which they can not be 
stressed without collapsing and being permanently deformed. 
Strain is the deformation produced by an over stress. 

Factor of safety is the ratio of the stress of collapse of a 
body to the maximum stress it is called upon to withstand. 
If, for instance, a body can stand a stress of 1000 pounds 
and it is used to stand only 100, its factor of safety is 10, 
that is, 1000:100 = 10. 

The determination of the factor of safety is a matter of 
great controversy among aeroplane designers, some choosing 
a factor of safety of 6 and others going as far as making it 15. 
Every designer gives apparently good reasons for the factor 
of safety adopted, but what really decides the question is 
the actual test, and while it is true that some machines can 
withstand successfully all kinds of over stresses, it is not less 
true that often they have been burdened with unnecessary 
weight. On the other hand, while machines built with a 
rather low factor of safety have given good account of 
themselves in the majority of adverse conditions, in some 
cases they have collapsed. This was due to the fact that 
the machines were built to stand the most common cases of 
abnormal stresses, leaving out of consideration the excep- 
tional ones. Evidently, this is not a good assumption, 
because the fact that they do not occur frequently is no 
excuse for their exclusion. 

The calculation of the factor of safety is based on the case 
of a machine in horizontal flight in calm weather, in which 
case the load supported by the wings is normal and equal 
to the weight of the machine, excluding the wings, whose 
weight is directly distributed over the pressure surface and 
thus they form the support for the rest of the machine. 
With this as a basis, are then calculated the greater stresses 



60 AVIATION 

due to the various atmospheric disturbances and to the 
evolutions, which a machine is called upon to perform. 

The air is very far from being a smooth and evenly flowing 
element; it contains gusts, eddies and upward and downward 
trends, which constantly assail a machine from all directions 
and against which the designer must provide, as he must 
also provide for the abnormal stresses brought about by 
banking, looping and flattening out, all of which impose 
upon the machine loadings considerably in excess of the 
normal. 

Another case to be considered in figuring the factor of 
safety is the reversal of loading or top loading, when the 
load of the wings is reversed in direction and exceeds that 
of normal flight. 

A machine built with a reasonable margin of safety will 
remain sufficiently under control even if some small structural 
part breaks during flight and will allow the aviator enough 
time to land without a smash. 

Everything considered, it would seem that a factor of 
safety of 10 is well suited to provide for all eventualities. 

Wood. — Wood is a very unreliable material, its strength 
varying considerably with the age of the tree, the season 
when it was felled, the geographical situation, the manner of 
seasoning, that is, if natural or artificial, and the different 
artificial method and size of the pieces used when seasoned. 
For this reason, the factor of safety of wood is about double 
that of metal. 

Wood has great tensile strength and generally is more 
flexible than steel tubing, but one of the chief obstacles in 
the use of wood is the difficulty of finding it in sufficient 
lengths without any blemishes; then it becomes necessary 
to join the good pieces together in laminations, that is, to 
glue strips of wood alternating the joints. The glue in this 
case must be insoluble, otherwise the strips will fall apart 
through dampness. A special kind of lamination is the ply- 
wood, which is made with very thin sheets or plies of wood 



AEROPLANE CONSTRUCTION 61 

glued together with the grain of one ply running across 
that of the other, thus forming a light, tough sheet. 

The woods most used in aeroplanes are: spruce, ash, white 
pine, cedar, walnut, mahogany and oak. 

Ash is a heavy wood, but it is also very strong and able 
to stand all stresses. Spruce is lighter than ash, but it stands 
only the stress of compression, and if bent or twisted, it 
splits easily. White pine is very light and does not split. 
Cedar is usually employed in the construction of pontoons, 
being well able to stand the action of water; mahogany is 
also used for pontoons, but it is very expensive. Walnut, 
mahogany and oak are generally used for propellers; the 
best of the three being mahogany, as it is the lightest and 
has the greatest tensile strength. 

Each kind of wood is used according to its peculiar be- 
havior in regard to flexibility, strength, lightness or hardness, 
but in aeroplane construction, the same kind of wood is not 
always used for the same part and, consequently, only 
general rules can be given. 

The spars are usually made of ash, spruce or an ash-spruce 
combination, and they are hollow at the neutral axis, but 
solid where the compression ribs, struts and wires are at- 
tached. 

The ribs are of spruce or of a combination of spruce for 
the cap strips and ash three-ply for the webs. 

The leading and trailing edges are spruce, although metal 
is more commonly used for the latter. 

The struts are generally spruce. 

The longerons and skids are ash. 

The engine rails are ash or laminated ash and spruce. 

No matter what the kind of wood used, as a general rule, 
the parts of an aeroplane which must stand a greater stress 
than others are made of stronger, harder and heavier wood. 
For this reason, the engine rails, which must carry the weight 
of the motor and stand its vibrations, must be made of very 
strong wood. The longerons, also, must be made of strong 



62 AVIATION 

wood, able to stand all stresses without breaking, because, 
as we have already seen, a damaged longeron means the 
taking apart of the fuselage and, as a consequence, of the 
whole machine. 

Metal. — The metal mostly used is steel, and that this is 
the best metal there is no doubt, as it withstands successfully 
all kinds of stresses. 

The main reasons against the use of steel are: its weight, 
its liability to rust, the difficulty of obtaining the point of 
union of the component parts as strong as the components, 
and the fact that steel tubing, as generally used in aeroplane 
construction, while giving great rigidity, does not permit 
of great flexibility, as in a thin tube all the material is at the 
surface, far from the neutral center, and if bent, it breaks 
right through. For these reasons, wood has been generally 
preferred, but the modern tendency is toward its elimina- 
tion, due to the introduction of non-rusting steel alloys, 
improved welding processes and more accurate calculation 
of the strength of the parts. The introduction of chrome 
nickel steel has increased the possibility of all metal con- 
structions, which possess greater strength and homogeneity 
and permit the standardization of the parts. 

Another non-rusting alloy which is now being tried, and, 
it seems, with good results, is the Monel metal, which is an 
alloy of 60 parts of nickel, 35 of copper and 5 of iron. 

As the metal which on account of its lightness is the first 
to be thought of by the aeroplane builder is aluminum, a 
comparison between aluminum and steel is not out of place. 
While the specific gravity of aluminum is about one-third 
that of steel, its tensile strength is about one-sixth, so that 
in reality we ought to use six times an amount of aluminum 
to have the same tensile strength of steel, which consequently 
would double the weight of the material and increase the 
size of the parts, causing more passive drift. Then again 
aluminum is not very cohesive and its bending strength 
is very bad, a fact which forbids its use, especially when 



AEROPLANE CONSTRUCTION 63 

it must be subjected to vibrations. In conclusion, out of 
the comparison, steel is the winner. 

In aeroplanes, as built to-day, the metal used is mostly 
steel in the form of wires, fittings and seamless tubing; and 
of such additional accessories as turnbuckles, ferrules, 
thimbles, fair leads, bolts, nuts, washers, rivets, clevis pins, 
cotter pins, tacks, screws and metallic sheets, in whose 
manufacture other metals are also employed. 

The wires are solid and stranded. Solid wire is used in 
parts of the machine which are not dismantled, because a 
solid wire can hardly be handled without kinking it and a 
kink means a weak spot, which, if strained, will break. 
The stranded wire is of three kinds: strand stay, which 
consists of from 7 to 19 wires stranded together; cord stay, 
which is made with 7 strands of from 7 to 19 wires to each 
strand; and control cable, which consists of 6 strands of 7 
wires each and a cotton center. The strand stay and cord 
stay are used in all parts of the machine which must be 
handled in assembling, disassembling and adjusting, because 
they are flexible and can easily be coiled without kinking 
.them. The control cable is used for the controlling planes, 
as it is very flexible and can easily go around pulleys. 

The fittings are made of pressed steel and are used to con- 
nect all the parts of the machine and for the attachment of 
the wires. 

Seamless steel tubing is employed for edges of controlling 
planes, for rudder and skid posts, for axles, struts and re- 
enforcements. 

Turnbuckles are usually made with two kinds of material: 
the barrel is bronze and the shanks steel. A turnbuckle 
(Fig. 39) is an important little device, which must be handled 
with care, because it is not so strong as it looks. First of 
all, pliers must never be applied to it, as the barrel is hollow 
and may easily be distorted or even cracked without showing 
any outside sign. If it is distorted, the threads will be spoiled 
and the shanks will not work freely, and if cracked, it may 



64 



AVIATION 




Fig. 39 



snap while the machine is in flight and cause a disaster. 
The proper way to operate a turnbuckle is to insert a stiff 
wire or nail in the hole of the barrel and another in the eye 
of the shank connected to the wire to avoid it from turning. 
Whenever a turnbuckle is un- 
screwed to disconnect a wire, 
the barrel must be screwed to 
the shank attached to the wire 
for a distance sufficient to avoid 
its occasional unscrewing and 
loss. When the wire is to be 
connected again, the barrel 
must be unscrewed all the way 
out, then screwed to the shank attached to the fitting just 
enough to catch it, the other shank brought to the other end 
and then the barrel turned, thus tak- 
ing in both shanks evenly. If this rule 
is not observed, one of the shanks 
will be all the way in the barrel, coming 
to the end of its run, while the other 
shank is almost all out, and this will pre- 
vent the proper adjustment of wires 
which are cut the right length to be 
properly tensioned by the turnbuckles. 
After a wire has been adjusted, the 
turnbuckle must be locked to avoid it 
from turning. This is done by insert- 
ing a wire A in the hole of the barrel, 
winding both ends around the barrel in 
a sense opposite to its unscrewing di- 
rection, passing the ends through the 
eyes of the shanks and winding them 
on the shanks. lg ' 

The ferrules are of two kinds: solid and wire. A solid 
ferrule (Fig. 40a) is a short tube, usually of copper, flattened 
enough to make it oval. A wire ferrule (Fig. 406) is made 



cu 







AEROPLANE CONSTRUCTION 



65 



with a wire coiled in a spiral and flattened to become oval. 
These ferrules are used in connection with the looping of a 
solid wire. 

A thimble (Fig. 41) is an almond-shaped steel eye used in 
the inside of a stranded wire loop, to protect it from the wear 
caused by the fric- 
tion of the shank. 

A loop is the doub- 
ling of a wire in such 
a manner as to form 
an eye for the reception of a turnbuckle shank or the pin 
or rivet of a fitting. 

With a solid wire, only one kind of loop can be made, 
that is, the ferrule and loop (Fig. 42), which is fastened by 
means of a ferrule and by bending the end of the wire. 




Fig. 42 




Fig. 43 

With a stranded wire, three kinds of loops can be made: 
the wrapped and soldered loop, the thimble and loop wrapped 
and soldered and the spliced loop. The wrapped and soldered 
loop (Fig. 43) is made by winding fine copper wire around 




Fig. 44 

the stranded wire at the part where it is to be looped, to 
protect it from wearing, doubling it, continuing to wrap 
both the wire and its doubled end and soldering the entire 
loop. The thimble and loop wrapped and soldered is made 
by inserting a thimble in the loop (Fig, 44), wrapping its 



66 



AVIATION 



end with copper wire and soldering loop and thimble. The 
spliced loop (Fig. 45) is made in a way similar to the thimble 
and loop, with the difference that the end of the wire, instead 
of being soldered, is unwound and its component strands 




Fig. 45 

inserted repeatedly in the wire and, finalty, served with a 
fine string or wire for further protection. 

Of the loops made with a stranded wire, the spliced loop 
is to be preferred for the absence of solder, because the 
soldering process requires the employment of acid, which 
filters into the wire and in due time will corrode it, causing 
it to break when the least expected and bringing about acci- 
dents. The spliced loop weakens the wire at the end of the 
splice, due to its kinking in splicing, but this loop will at 
all times give a warning of its weak condition and can be 
replaced in time to avoid damage. 

Fair lead (Fig. 46) is a short copper tube with the ends 
enlarged funnel-like to prevent its edges 
from cutting and is used for the passage 
and guide of control cables. 

The bolts used in aeroplanes have a hole 
at the point (Fig. 47a) for the introduc- 
tion of a locking cotter pin; the nuts are usually castel- 
lated (Fig. 476), that is, they have grooves at their 
upper face to receive a cotter pin; the washers (Fig. 47c) 
are disks with a hole in the center for the passage of a 
bolt; the rivets (Fig. 47c?) are short bolts without thread, 
used to lock parts together by burring the edge of the 
point; clevis pins (Fig. 47c) are rivets with a hole at the 
point for the passage of a cotter pin; the cotter pins (Fig. 47/) 




Fig. 46 



AEROPLANE CONSTRUCTION 



67 



are split keys made by bending a half round wire with the 
flat face inside, so as to form an eye at the bend and bring 
together the two halves or leaves, which thus make a round 
wire open in the middle, and they are used in holes of clevis 






Fig. 47 

pins to lock them by spreading out the leaves or to lock the 
nuts of bolts provided with an opposite hole at the threaded 
end. All these parts are made of steel. 

The tacks, usually barbed (Fig. 47gr), and the screws are 
copper or brass and are used to fasten fabric on wood or 
wooden parts together. 

Metallic sheets of aluminum or galvanized tin are usually 
employed for stream-lining purposes. 

Fabric. — The best fabric used for covering the planes is 
unbleached Irish linen, because the thread of the flax, which 
is used to make it, is about two feet long and thus provides 
a good overlapping margin when it is spun, forming a very 
strong cloth. It is left in its natural color to be stronger, 



68 AVIATION 

because the bleaching chemicals weaken the fabric. Irish 
linen weighs about 4 ounces per square yard and stands a 
load of over 60 pounds per linear inch of warp. Sometimes 
cotton, silk or a combination of both is used for plane cover- 
ing, as cotton alone does not make a strong fabric, its threads 
being very short, and silk, although light and very long 
threaded, has the fault of absorbing moisture, besides being 
very expensive. Sea Island cotton is also used with good 
results, its thread being about as long as that of Irish linen. 

There are two methods in use for covering the wings with 
fabric. One consists in throwing a large sheet of cloth on 
the frame, tacking it temporarily on one edge, passing the 
cloth around, tacking it permanently in place at all the edges 
and ribs and sewing it around the ribs. The other method is 
to be preferred, because it is easier and gives better results. 
It consists in cutting the fabric in the shape of -the wing, 
sewing the edges around and turning it inside out, forming 
a kind of a bag, in which the frame is slipped and the mouth 
of the bag tacked permanently at the root end of the wing. 
The fabric is then tacked with as few tacks as possible on 
the under camber of the ribs. The wing is stood on the 
leading edge, additional strips of fabric laid on both sides of 
the ribs and both strips and fabric sewed around the ribs 
with about four loops of thread, which are repeated at a 
distance of a couple of inches. This gives the proper shape 
to the fabric, but does not make it very tight and to accom- 
plish this result, it is painted with dope, and then an extra 
strip of cloth doped on each side of the ribs to cover the 
stitches. 

Dope is cellulose nitrate or acetate dissolved in banana 
oil. Cellulose nitrate is the same compound of guncotton 
and is therefore highly inflammable, while the acetate is 
less inflammable. Banana oil is a mixture of acetone and 
amylacetate with liquid celluloid. As the vapor of the solv- 
ent is inflammable and volatile, care should be taken not 
to have an open fire in close vicinity of the dope container 



AEROPLANE CONSTRUCTION 69 

and not to leave it uncovered or the dope will thicken, due 
to the evaporation of the solvent. Dope will thicken also 
at a low temperature. If the thickening is due to evapora- 
tion, the dope can be brought to its normal flow by adding 
the right amount of solvent, but if caused by the tempera- 
ture, it is only necessary to warm it for a short time by putting 
the container in some warm place. 

The brushes used for the dope must be kept immersed in 
it or they will stiffen, in which case it is necessary to stand 
them in it until they become soft again. 

If the fabric to be doped, as well as the brushes and dope 
cans, are not clean, dry and free from oil or grease, the dope 
will not adhere well and will peel off when dry. Fabric soiled 
with greasy matter can be easily cleaned by rubbing it with 
a piece of cloth moistened with gasoline or acetone. 

In doping new fabric, the first coat is applied with a light 
pressure on the brush to cause the dope to filter through, but 
all successive coats must be applied lightly and quickly with- 
out brushing out as is usual with paint, otherwise the previous 
coatings will be cut. Every coat must be dry and scraped 
with steel wool to even up the dope before the next coat is 
applied. Four coats of dope are required to make the fabric 
very tight and airproof . To render the dope less inflammable 
and make it waterproof, two coats of spar varnish are given. 

Spar varnish is a dense, but clear and easy flowing, yellow 
liquid, which dries quickly with a lasting luster. It is the 
best kind of varnish for exterior work, being waterproof, 
elastic, durable and able to stand the effects of grease, oil, 
rain, hot and cold, fresh or salt water, extreme or sudden 
variation of temperature, without cracking or changing its 
color, and for these reasons, it is used on boats as a protective 
coating for wood, metal and fabric. 

A change of color in a varnish is a sign of deterioration, 
because it then becomes porous and allows the harmful 
elements to filter through and attack the materials which 
it is intended to protect. 



CHAPTER III 
RIGGING 

Assembling 

Fuselage. — To assemble a machine, the first thing to do 
is to place the fuselage in the position necessary to attach to 
it all the other main parts. To this effect, the tail skid is 
connected by pinning it to the socket of the tail post or in- 
dependent skid post and tying the shock absorber. The 
front part of the fuselage is then lifted on a wooden horse 
high enough to allow the undercarriage to be fitted to it. 
In lifting the fuselage, care must be taken not to damage it, 
and if block and tackle is used, the hook of the block must 
be attached to a line passed under the engine rails. 

Undercarriage. — After mounting the wheels on the axle, 
the undercarriage is pushed under the engine section of the 
fuselage until the fittings correspond to the struts, which are 
put in place and bolted. The cross bracing wires are then 
connected and the fuselage tail is raised and supported on a 
horse, so as to assume the rigging position. The shock ab- 
sorbers are wrapped in place and tied. 

Center Section. — The center section struts are bolted in 
their sockets on the fuselage, the panel mounted and bolted 
to the struts, and the cross bracing wires and drift and anti- 
drift wires attached in place. 

Wings. — The ailerons are removed to prevent any possible 
damage and facilitate the work, and the wings assembled 
in pairs by standing them on the leading edges, which must 
rest on cloth or cushions to avoid damaging the fabric on 
the nose of the wings. The two wings are spaced apart the 
proper distance, the front and rear struts bolted in their 
70 



RIGGING 71 

sockets, the stagger and incidence wires attached first, to 
prevent the wings from wabbling, and then the front and 
rear flying and landing wires are connected to make the 
structure rigid. The wings are now lifted bodily and con- 
nected to the center section by means of the top and bottom 
hinges and pins and the inner landing and flying wires. The 
first pair of wings must be supported by a horse placed di- 
rectly under the outer struts until the second pair is con- 
nected. The ailerons are then mounted by means of the 
hinges and pins. 

Great care must be taken in handling the wings to avoid 
damage and they must never be lifted by taking hold of the 
struts or trailing edges. The best way is to lift them by 
means of wooden boards, placing blocks between the boards 
and the spars, which thus carry the load. 

The top pins are put in place first, because they are enough 
to hold the wings and in the meantime facilitate the intro- 
duction of the lower pins. The front struts and flying and 
landing wires are attached before the rear ones to make the 
work easier, as the latter would be in the way, if they were 
put in place first. 

In dismantling the wings, the mounting process is re- 
versed, by starting to detach first the part that was attached 
last. 

To facilitate the assembling of the wings and prevent 
errors in mounting, the struts are numbered, and although 
the system varies with different manufacturers, the numbers 
are always painted on the inside part of the struts, to enable 
the aviator to see them from his seat and easily detect any 
error of position or inversion. 

As a general rule, when a part has been assembled, the 
nuts of the bolts are screwed tight, cotter pinned and the 
leaves of the pins spread backward. The hinge pins are 
also cotter pinned in the same way. 

When possible, the bolts are put in place with the point 
downward, so that if a nut should come loose, the bolt would 



72 AVIATION 

not fall; although this must not be an excuse for carelessness 
on the part of the rigger to omit the pinning of the bolts. 
Whenever the position of a bolt is not vertical or inclined, 
so that this rule can not be followed, then the nut is placed 
on the inside, to be easily seen by the aviator from his seat. 

Empennage. — The horizontal stabilizer is bolted in place 
and the bracing wires or struts attached on both sides. The 
vertical stabilizer is bolted on the horizontal stabilizer and 
the bracing wires attached on both sides. The rudder is 
mounted on the rudder post by means of the hinges and 
hinge pins. The elevators are connected with the horizontal 
stabilizer in the same way as the rudder. 

Control Wires. — The control wires of the ailerons, ele- 
vators and rudder are connected by means of the turn- 
buckles. 

Truing 

In truing up an aeroplane, the basis of all adjustments 
is the manipulation of the cross bracing and opposite wires, 
that is, the slackening of one and the tightening of the other 
to properly reshape parts thrown out of true. 

To facilitate the work, the angles are measured in inches 
instead of in degrees, as they ought to be measured. 

The right and left side of an aeroplane and the clockwise 
and anticlockwise revolution of a propeller are determined 
by the position of the aviator sitting in the machine. 

The following rules for truing up an aeroplane are in- 
tended for field shop work, which is quite different from that 
done in the factory, where the rigger has at his disposal all 
the necessary equipment and tools to obtain the best results 
in the least time. 

Fuselage. — To true up an aeroplane, the first thing to do 
is to place the fuselage in the rigging position (Fig. 48), 
which is done by leveling the engine rails longitudinally and 
laterally, as they are the basis of the alignment of all parts. 
To accomplish this, a horse is placed under the fuselage, 



TUGGING 



73 



immediately in the rear of the engine section, so that' the 
center of gravity of the fuselage will be toward its rear and 
the tail will have a tendency to fall to the ground. While 
the tail is being supported temporarily, a chain is tied to the 



-SP/xrr terse 



\ h \s&a*\ a 



7f 




Fig. 48 

nose plate and to an eye fixed to the floor. This will keep 
the fuselage in place with the tail sticking out unsupported. 
To facilitate the work, the chain has a turnbuckle to raise 
and lower the fuselage any desired amount. A level is now 
placed laterally on both engine rails and the fuselage leveled 
crosswise by inserting a wooden wedge between the fuselage 
and the top rail of the horse at the side which needs to be 
raised. This done, the level is placed longitudinally on one 
of the engine rails and the fuselage leveled lengthwise, moving 
it up or down by means of the turnbuckle. The level is then 
placed on the other engine rail, which, if it is true, should 
also be level; if it is not, it must be adjusted by means of the 
side cross bracing wires of the engine section, loosening one 
and tightening the other the necessary amount. Then, the 
centers of the bottom struts of the engine section are marked, 
a line stretched from the center of the first to that of the 
last strut and the bottom cross bracing wires manipulated 
until the line cuts all center marks. The next thing is to 
level the fuselage from the rear of the engine section to the 
tail. To do this, all the internal cross bracing wires must 
first be slackened, otherwise they bind the manipulation of 



74 AVIATION 

the other wires; then both longerons are leveled longitudin- 
ally by sighting them and correcting roughly by eye any 
up and down distortions by manipulating the cross bracing 
wires, after which the level is placed longitudinally on the 
longerons to straighten them out properly by the use of the 
same wires. 

To correct any sidewise distortion, the top and bottom 
cross bracing wires are used respectively. This work is 
done by measuring and marking the centers of all top and 
bottom struts and stretching lines from the centers of the 
last top and bottom struts of the engine section to the rudder 
post, and adjusting the top and bottom cross bracing wires 
until the lines cut all the center marks on the struts. 

The internal cross bracing wires are now tightened, while 
the level is placed transversally on the longerons to avoid 
throwing them out of level in tightening the wires improperly. 

The above rules hold true with a machine having the line 
of thrust parallel with the top longerons; if this is not the 
case, special rules must be furnished by the manufacturer. 

The assumption has also been made that the motor is 
not in place on its bed; if it is, then the level must be placed 
on any available part of the engine rails, and, if it need be, 
even held against their bottom. 

Undercarriage. — In case of a new machine, the front and 
rear cross bracing wires must be manipulated until they 
have the same length and tension. With an old machine, 
this system can not be applied, as the fittings may be dis- 
torted or the heads of the bolts sunk unevenly into the wood, 
and the length of the wires may not be the same, although 
the undercarriage may be aligned. 

A method applicable to all machines is to mark the center 
of the fuselage at a point directly above the axle of the wheels 
and the center of the axle or the spreader (Fig. 49), then to 
drop a plumb line from the upper mark and adjust the cross 
bracing wires until the point of the bob is over the center of 
the axle. If there is no part available on the fuselage to 



RIGGING 



75 



mark its center, a yard stick may be laid on the longerons 
and the center taken from there. 

Center Section. — The center section is trued up in a way 
similar to that of the undercarriage, that is, by marking 
the centers of the leading and trailing 
edges or front and rear spars of the 
center section panel and the centers of 
the struts below them on the fuselage 
or by using yard sticks in the absence 
of struts (Fig. 50a). The center sec- 
tion is then aligned by manipulating 
the front and rear cross bracing wires 
until the points of the bobs of the Fi S- 49 

plumb lines dropped from the upper center marks are di- 
rectly above the lower ones. 

If the machine has a stagger, a plumb line is dropped from 
the leading edge of the center section panel in front of each 
strut (Fig. 506) and the measurements taken in front of 
the bottom sockets of the same struts, adjusting the drift 
and antidrift wires until the proper distances are obtained. 






Fig. 50 

Wings. — Leading edg<\ To make any adjustment in the 
wings, the first thing to do is to slacken the stagger and 
incidence wires, otherwise they bind the manipulation of 



76 



AVIATION 



the other wires. This done, the leading edges of the wings 
are aligned by standing on a ladder some distance away 
from the machine, sighting along the leading edge of each 
top wing separately and straightening it by means of the 
front landing and flying wires of the outer bay. The manipu- 
lation of these wires straightens also the leading edges of 
the lower wings. 

When a machine has an overhang, its wires must be used 
too in the straightening process. 

After the wings are straightened, they must be brought 
in line with the leading edge of the center section panel by 
manipulating the landing and flying wires of the inner bay. 

The reason why the outer bay wires are used to straighten 
the wings is because one end of each wire is attached to the 




Fig. 51 

spar of the upper wing and the other end to the spar of the 
lower wing between struts, thus bracing the rectangular 
framework formed by the spars and struts and rendering 
possible their adjustment; while only one end of each wire 
of the inner bay is fixed to the spar, the other being fastened 
to the center section or the fuselage, making possible only 
the raising or lowering of the wings. In the entire straighten- 
ing and aligning process, only front wires are used, because 
the rear are manipulated to set the angle of incidence. 

Lateral Dihedral Angle. — To set the lateral dihedral angle, 
one end of a line is tied to the outer front strut of one wing 



RIGGING 77 

(Fig. 51), then passed over both wings along the front spar, 
stretched enough to avoid sagging and tied to the outer 
front strut of the other wing. The measurement is taken 
from the line to both sides of the center section panel, and 
the landing and flying wires of the inner bay are manipulated 
until the proper distance is obtained. 

Care must be taken to measure from both sides of the 
center section, because if the distance is measured at the 
center, the dihedral angle may be set wrong, as the wings 
may not have been raised equally on both sides and while 
one is higher than the other, the center may give the proper 
distance. 

The hidedral angle may be checked by taking measure- 
ments from the center of the leading edge of the center 
section panel to equal points on both sides of the wings; 
for instance, from that center mark A to the lower sockets 
of the inner struts B, B', or the outer struts C, C '. If the 
dihedral is right, each pair of distances must be equal, 
A B = A B', A C = A C". 

Angle of Incidence. — The angle of incidence is checked 
at the root end of the wings and measured under each set 
of struts by placing 
against the center 
of the rear spar one sntAnur ™< 

end of a straight 
edge (Fig. 52), level- 
ing it out and measuring vertically from the center of the 
front spar to the top of the straight edge. The proper dis- 
tance can be given by manipulating the rear flying and land- 
ing wires. The front landing and flying wires must not be 
touched, as this would throw off the adjustment of the 
wings, both in regard to straightness and alignment with 
the center section panel or dihedral angle, if any. 

The angle of incidence is never measured from the trailing 
edge or between the struts, as the possible warping of these 
parts may give a wrong measurement. 



Fig. 52 




78 AVIATION 

Stagger. — The stagger is set by dropping plumb lines 
from the leading edges of the upper wings in front of each 
strut (Fig. 53) and making the distance specified equal 
throughout, by measuring from the lower edges to the plumb 

lines and manipulat- 
ing the stagger and 
incidence wires ac- 
cordingly. 

Care must be taken 
in de t e rmini ng 
whether the specified 
g " distance is to be meas- 

ured along the chord or a horizontal distance straight out, 
as this causes a difference which is enough to unbalance a 
machine. 

Wash in and wash out. — To correct the direct effect of the 
propeller torque, the angle of incidence is changed usually 
at the wing tip under the rear outer strut, but in some ma- 
chines it is tapered down from the tip to the root of the 
wing by adjusting the angle under both rear struts. 

Aileron Droop. — The ailerons are drooped by lengthening 
the balance wire and taking the required measurement 
from the bottom of the rear edge of 
the wing to the bottom of the rear 
edge of each aileron. The droop is 
given for the reason that when the 
machine is in flight, the pressure of 
the air under the ailerons takes up 
the slack and brings them in line 
with the wings. lg ' 

Empennage. — The horizontal stabilizer A (Fig. 54) must 
be in a horizontal position, which is determined by bolting 
it in place properly and adjusting its side bracing wires B 
and C. 

The vertical stabilizer D (Fig. 54) is aligned by adjusting 
its side bracing wires E and F until it is vertical. 




RIGGING 



79 




With the control column in its neutral position, the control 
cables are adjusted until the elevators A (Fig. 55) are on 
a line with the horizontal stabilizer B, using for this a straight 
edge C under them 
both or sighting 
them. 

With the foot rud- 
der bar in its neutral 
position, the control wires are adjusted until the rudder A 
(Fig. 56) is at right angles with the rear edge of the horizon- 
tal stabilizer B. 

The rules regarding the rudder and elevators do not take 
into consideration the correction of the indirect effect of the 
propeller torque, nor the drooping of the elevators; if these 
adjustments must be made, the following process is available: 

If the propeller torque is corrected by means of the vertical 
stabilizer A (Fig. 57), the rigger has nothing to do with it, 
its mere bolting in place giving the necessary position. 

To set the rudder at an angle to the right A (Fig. 58) or 




Fig. 57 

left, a line B C is stretched from the vertical stabilizer D 
to the rudder and, keeping the foot rudder bar neutral, the 
control cables are so adjusted as to make one so much shorter 



80 



AVIATION 



than the other that the rudder will form an angle a with the 
line, the given distance being measured from the rear edge 
of the rudder to the line. A 
straight edge may be used in- 
stead of a line. 

To droop the elevators, a 
line A B (Fig. 59) is stretched 
over the top and on each side 
of the horizontal stabilizer C, 
in such a way as to follow its 
camber, and the droop meas- 
ured from the upper side of the 
rear edge of each elevator D to 
the line. 

As a general rule, whenever 

an aeroplane part is trued up, 

c the turnbuckles are locked. 

Fi s- 58 Controls.— The control cables 

must be so adjusted that by moving the controls sharply 

about 1/8 of an inch, the motion must be transmitted to 

the controlling planes without stiffness or slack. The control 




Fig. 59 

mechanism, pulleys and hinges, as all other moving parts 
of the machine, must be well lubricated with graphite to 
work freely and smoothly. 



Rigging Care and Faults 

The greatest care must be exercised in handling all parts 
of the machine in assembling and truing them up, to avoid 
damage, and in adjusting them properly. 

In truing up an aeroplane, a great deal depends on the 
perfection of the tools used and the way they are nandled. 



RIGGING 81 

The adjustable end wrenches, for instance, must have the 
right opening and the fixed end wrenches must be the proper 
size in operating the nuts, otherwise they will round their 
edges and spoil them. The levels and straight edges must 
be perfect, and to make sure of this, they must be tried 
before using them. To this end, the straight edge is clamped 
lightly in a vise and leveled, then the level is reversed on 
exactly the same place and the bubble watched carefully to 
see if it marks center again, in which case, it is moved slowly 
along the entire length of the straight edge to ascertain if it 
is perfectly straight throughout. The line used for the ad- 
justment of the dihedral angle must be well stretched to 
prevent it from sagging and giving a wrong measurement. 

The wires must be given the proper tension: if they are 
slack, the adjustments of the parts to which they are at- 
tached will be thrown out of true when under tension; and 
if they are too tight, they distort the parts and cause bending 
stresses, which are the most dangerous in an aeroplane 
framework. For the same reason, in handling a machine, 
care must be taken never to produce bending stresses, es- 
pecially with struts. If an aeroplane is to be moved about, 
the points to be taken hold of are either the lower parts of 
the interplane struts or the upper parts of the undercarriage 
struts. Some machines have hand holes at the wing tips 
to facilitate their handling without damage. Special care 
must be had not to use the trailing edges of the wings as a 
holding point to move a machine, as they are weak and 
break easily. 

The turnbuckles must be well lubricated, must work freely, 
but not loosely, and must be properly locked soon after the 
adjustments of the wires to prevent their slackening. 

All nuts must be closely cotter pinned, that is, the pins 
must be very close to the nuts to avoid their loosening. 

The controlling planes deserve special consideration in 
mounting and truing them, because they are essential to the 
safety of the aviator. 



82 AVIATION 

The engine rails must be leveled with the greatest of care, 
as they are the basis of all other adjustments and the slightest 
error in them throws the entire machine out of true, espe- 
cially at the tail end, where the error will be greatly in- 
creased. 

The balance of the machine depends on the way it is trued 
up. If, for instance, the angle of incidence is smaller or 
greater than it should be or the stagger improperly adjusted 
or the fuselage distorted downward or upward, the longitud- 
inal stability will be affected and the machine will fly tail 
high or tail low. The lateral stability is affected by setting 
the wings at a different angle of incidence, thus causing one 
wing to fly low and consequently the other high, owing to 
their different lifting power. This same fault causes the 
machine to swing around, due to the difference in the drift 
of the wings, thus unbalancing the machine directionally. 
If the fuselage is distorted sideways, the machine has a 
tendency to circle around, as, in this case, it will be offering 
more keel surface on one side than on the other. If the con- 
trolling planes are not set at the proper angle or they are 
distorted, the control will be inefficient. If the angle of in- 
cidence of the wings is greater than it ought to be, besides 
unbalancing the machine longitudinally, causing it to fly 
nose high, it will produce poor flight speed, due to the in- 
creased resistance. 

In conclusion, every error in truing is felt by the aeroplane, 
and too much emphasis can not be laid on the fact that the 
adjustments must be scrupulously exact. 



CHAPTER IV 
PROPELLERS 

Theory. — Propeller and mystery are synonymous. In our 
Year of Grace 1919, nobody knows exactly what a propeller 
is. This being the condition of things at the present day, 
we can only accept with the benefit of doubt whatever in- 
formation we can gather in regard to propellers. 

The original theory considers the propeller a section of a 
screw arid therefore the blades portions of the thread; which 
means that the propeller, in revolving, screws itself into the 
air and converts its rotary motion into a linear motion. The 
reason why only a portion of the thread is used is that a 
small slice of it is found sufficient for propeller purposes. 
The number of sections used represents the number of blades, 
which are made much longer than the thread, because in 
this way they are more efficient. 

The theory most commonly accepted to-day is based on 
the analogy of the propeller blade with a plane, the difference 
being that the plane moves in a straight line, while the blade 
moves in a circle, advancing in the meantime in a straight 
line and consequently describing a spiral path; in other 
words, the propeller blade is considered a revolving inclined 
plane, although even those who accept this point of view 
admit that it is not absolutely exact, but very useful as a 
basis for calculation, whose results conform very closely with 
those obtained by experiment. 

The new theory is, therefore, a modification of the old 
one, substituting a plane for a section of thread, but, ad- 
mittedly, the facts deny the principle. The outcome is that 
both theories are found wanting and in practice it is neces- 
sary to use empirical formulas to solve propeller problems. 
83 



84 AVIATION 

Another point of view taken by modern experimenters 
is the application of the reflection or batting theory, that is, 
the assumption that the blade in striking the air causes it to 
jump off at the same ang\e of entry and the reaction imparts 
a forward motion to the blade. Although this hypothesis 
is very plausible and seems to be in very close accord with 
facts, it is not sufficiently developed to be accepted just now 
and we are forced, therefore, to follow the mixed principle 
of the screw and plane. 

The capital difference between a screw working its way 
into a nut and a propeller screwing itself into the air is due 
to the fact that the air is not solid like the nut and the pro- 
peller blades can not get as good a grip on the air as the 
screw on the nut, the result being that the air slips back 
and the propeller can not advance the full distance it ought 
to according to the angle of the blades. This brings us to 
the consideration of three different quantities: the distance 
the propeller ought to travel, the distance it actually travels 
and the distance lost. If we consider these quantities for 
one revolution only, we will have the following definitions: 
theoretical pitch is the distance through which the propeller 
would advance in one revolution if it moved in an unyielding 
medium; effective pitch is the distance actually traveled in 
one revolution; slip is the difference between the theoretical 
and the effective pitch. 

The pitch depends on the angle of the blades or angle 
of pitch. 

If the pitch of every point of the blade of a propeller is 
to remain constant, the angle of pitch must increase as 
the hub is approached, because the nearer we get to it, the 
smaller become the diameters of the circles described by the 
propeller when revolving and, consequently, the smaller 
the circumferences of the circles. 

If we mark the points A, B, C (Fig. 60) on one blade of a 
propeller D and then we cause it to revolve on its axis just 
once without advancing, these points will describe circles, 



PROPELLERS 



85 



which will be smaller the nearer the point considered is to 
the hub E. From this, it is clear that the greatest circle is 
described by the propeller tips and the smallest by the center 
of the hub, where a circle is represented by merely a point, 




Fig. 60 

consequently the smallest angle is at the tips and the biggest 
would be at the center of the propeller, provided that we 
could build a propeller without a hub, and even if we could, 
the angle would be of no use whatever, as it would be prac- 
tically a right angle. 

To make this clear, let us consider the circles described 
by the points A, B, C, as the bases of screws having all the 
same length (Fig. 61). If we want these screws to advance 
their full length in one revolution in their respective nuts, 
it is evident that each one must have just one thread, starting 



86 



AVIATION 



at the top and ending at the bottom of the same side of the 
screw. If we wrap each screw with paper once around with- 
out overlapping the ends, mark 
on the paper the path of the 
thread and then unwrap and 
flatten it out, we find that the 
thread is the diagonal of the 
rectangle, which represents the 
development of the lateral sur- 
face of each screw (Fig. 62). 
If we now cut the rectangles along the diagonals, and take 
one-half of each one, we will have three right-angled triangles, 
whose respective height represents the distance advanced by 



/ 




/ 




( 


V 




\ 




y. 


/ 




) 




u 



£ 

Fig. 61 




Fig. 62 

each screw in one revolution or the pitch, which is equal in 
all three; the bases represent the developed circumferences 
of the circles of the bases of the screws and the hypotenuses 

represent the threads. 
The triangle thus formed 
is the triangle of pitch 
(Fig. 63). 

If we put these tri- 
angles one on top of the 
other, having the big- 
gest at the bottom and 
the smallest at the top, 




Ccr*cusnfer*en.ce 



Fig. 63 

in such a way as to make the heights coincide (Fig. 64), we 
see that the angles A, B, C are not equal, but C is bigger 
than B and B bigger than A. As each angle represents the 



PROPELLERS 



87 



angle of pitch of each screw, we see that the smaller the 
screw, the bigger is the angle of pitch and the steeper the 
pitch line which the thread 
must follow. 

A small section of each screw, 
cut across its longitudinal axis 
(Fig. 65), will act in the same 
way if screwed in its nut, be- 
cause the slice of thread left 
will work its way through the 
nut just the same as if the 
thread were in its entirety. 

We have come to this con- 
clusion by starting from the 
assumption that the points A, B, C were taken on the same 
propeller and, consequently, what we have found in the 
case of the screws of different diameters and equal heights 
applies to these points, and if we curve around the triangles, 
so that the bases form circles, and we put them one inside 
the other (Fig. 66), the hypotenuses indicate the pitch lines 




Fig. 64 




Fig. 65 

of the points A, B, C, that is, the spiral paths which they 
would follow respectively if the propeller advanced through 
the air. In other words, we may consider a screw propeller 
as composed of an immense number of screws one inside the 
other, out of which all the unnecessary parts have been cut 
out, leaving only the center screw as a hub and attaching 
to its thread the threads of all the following screws. This 
would give us only one blade, which, of course, can be re- 
produced, giving us the means of making a propeller with 
as many blades as desired; but, following the analogy of 



88 



AVIATION 




Fig. 66 



the propeller blade with the plane, the same law of inter- 
ference which limits the gap holds true, but only in so far 
as it is applicable to the propeller. 

In the case of superposed planes, we are free to make the 
gap the distance required or to stagger the planes, but with 

a propeller this is not 
possible, as the blades 
arc fixed both in po- 
sition and • distance, 
and the only thing 
left is to make the 
width of the blade 
proportional to the 
gap or vertical dis- 
tance between two 
consecutive helicoid- 
al paths in order to 
regulate the amount of compression and rarefaction caused 
by the camber of the propeller and avoid interference. This 
means that the greater the number of blades of a screw pro- 
peller, the smaller must be the width of the blades and, 
consequently, the greater their aspect ratio. 

The consideration of aspect ratio brings us to that of the 
diameter of the propeller, which is of the greatest importance, 
because a propeller of large diameter is more efficient in the 
utilization of power for several reasons. The thrust or 
power delivered by the propeller is concentrated on its blades 
and, therefore, the larger the area on which the thrust is 
distributed, the smaller its proportion for unit surface and 
the more able is the propeller to withstand the stress with- 
out breaking. To obtain the greatest efficiency, all parts 
of the blade should do the same amount of work, but as 
the angle of pitch increases towards the hub, the nearer we 
get to it, the smaller will be the thrust drift ratio, the greater 
the disturbance of the wash caused by the hub and the 
smaller the efficiency, so that the greatest quantity of work, 



PROPELLERS 89 

if not all of it, is done by about two-thirds -of the outer part 
of the blade, the inner part being designed for low resistance 
rather than for driving. An increase in diameter really 
means an increase in the efficient part of the blade, as the 
further out we go, the smaller we find the angle of pitch 
and the greater the thrust drift ratio and, consequently, the 
greater the efficiency. The efficiency of a propeller increases 
with the increase in diameter, because the area swept by 
the propeller increases with the square of the diameter, 
which results in a reduction of slip: the greater the diameter, 
the lower the speed necessary to run the propeller and in 
consequence of both the increased surface and the dimin- 
ished speed, the propeller gets a better hold on the air and 
does more useful work, reducing to a minimum the wasteful 
slip. 

While we can safely say that a screw propeller must have 
a large diameter to be more efficient, we must consider, on 
the other hand, the limit imposed by the strength and weight 
of the material. 

Another very important consideration is the proportion 
between the pitch and the diameter of a propeller or pitch 
ratio, which varies for different cases of service, a high-speed 
machine requiring a higher pitch ratio than a low-speed 
machine. To obtain the best efficiency, the pitch must be 
about 134 times the diameter, but when we take into con- 
sideration the diameter of the propeller, which must be as 
large as possible to be more efficient, the high speed of the 
gasoline motor and the relatively slow speed of the majority 
of the machines used to-day, we see that it is not always 
possible to obtain the pitch ratio of best efficiency, and we 
find that the propeller used at present for aeroplanes is of 
finer pitch than that of best efficiency. 

In the case of a machine whose flight speed is 50 M. P. H., 
with a motor running at the speed of 1100 R. P. M. and 
an 8-foot diameter propeller, we find that the effective pitch 
must be 4 feet, which is just one-half the diameter of the 



90 AVIATION 

propeller, instead of 10 feet, as it ought to be for best effi- 
ciency. If the flight speed of the machine were instead 125 
miles per hour, then the effective pitch would be 10 feet and 
the requirement of best pitch ratio fulfilled. From this, 
we see that as the speed of the machine increases, the in- 
compatibility between the speed of the motor and the pitch 
ratio decreases, and in the future, when all machines will 
have reached the highest speed, this incompatibility will 
be entirely eliminated. At the present, this could be ac- 
complished by gearing down from the engine to the pro- 
peller, but as this would cause a loss of about 4 per cent 
of the power and as the loss of efficiency with the direct 
coupled propeller is not great, the direct drive is preferred, 
especially as it produces a lower torque on the crank shaft 
and a consequent lower effect of the propeller torque on the 
machine. 

A screw propeller is usually designed for the greatest 
velocity of an aeroplane, so that for a diminution in speed, 
the efficiency of the propeller diminishes also. 

In laying out a constant pitch propeller blade, the first 
consideration is the determination of the blade angles at 
different radii as modified by the slip; then the centers of 
figure of the sections, which should all coincide with the 
axis of the blade; and, finally, the centers of pressure of 
the different sections, which should be so disposed as to 
avoid any twisting effect on the blade. 

A matter of controversial nature is the existence of cavita- 
tion in an aeronautical propeller. Cavitation would be the 
rarefaction of air produced in the space immediately in 
the rear of a swiftly revolving propeller blade, due to the 
rapid cleavage of the air by the blade and the relatively 
slow action of the air in closing in behind the moving blade, 
and while it is generally said to make its appearance at about 
1500 R. P. M., there are those who flatly reject the theory 
in the case of aeronautical propellers. Cavitation is ad- 
mitted by all to exist in marine propellers, and this, coupled 






PROPELLERS 91 

with the fact that the aspect ratio of a marine propeller 
blade is limited by the much greater pressure reaction due 
to the much greater density of the water as compared to 
the air, explains the lower efficiency of a marine propeller, 
which at most is about 75 per cent, while for aeronautical 
propellers is about 85 per cent. No material known to-day 
would stand the increased pressure due to an attempt at 
increasing the efficiency of a marine propeller, while for air 
propellers the use of the softest wood would compare far 
better. 

In regard to the position of the propeller in front or in 
the rear of an aeroplane, there are advantages and disad- 
vantages in either case. 

The power used to drive the machine forward is spent in 
imparting a forward motion to the air, so, if we place the 
propeller at the rear, it will be running in air which is al- 
ready moving forward at a great rate of speed and this has 
the effect of greatly reducing the slip, and if the slip should 
be equal to the forward motion of the air, then the apparent 
slip, that is, the difference between the velocity of the pro- 
peller and the velocity of the machine, would be zero and 
the machine would be flying just as fast as if the propeller 
were screwing its way through a solid medium. It may 
happen, and it has already actually happened with steam- 
ers, that the forward motion of the fluid in which the 
machine is running is greater than the slip, and in this 
abnormal case, the machine would be going faster than 
if the propeller were running in a solid nut. This is 
the case of negative slip, that is, the velocity of the ma- 
chine is greater than the velocity of the propeller. But 
while these are merely theoretical considerations, some 
of which may or may not materialize, the fact remains, as 
we have already seen, that a propeller in the rear means a 
specially constructed and clumsy fuselage, with attendant 
outriggers, struts and wires, which increase the weight and 
the drift of the machine, probably eliminating altogether 



92 



AVIATION 



the advantages of having the propeller in the rear. When 
the propeller is in front, the fuselage can be built in the best 
stream-lined shape, which reduces the resistance and weight 
to a minimum, and besides, due to the fact that the air is 
blown against the wings, the lift is more than doubled, both 
because the speed of the machine relatively to the air is 
increased and because more air is engaged, and we know 
that the lift is proportional to the amount of air engaged 
and to the square of the velocity. While this is a great ad- 
vantage, it is in the meantime a great disadvantage, be- 
cause the air blown against the machine has also the effect 
of pushing it backward, so that the effective forward motion 
is the difference between the two forces; and although the 
increased lift enables us to reduce the span, on the other 
hand, the increase in passive drift requires the employment 
of a considerably greater horse power. 

Problems. — To find the angle of pitch at a given point of 

a constant pitch pro- 
peller, it is necessary 
to know the pitch, and 
vice versa; that is, to 
find the pitch, we must 
know the angle. 

If the pitch of a pro- 
peller A (Fig. 67a) is 
6 feet and we want to 
find the angle of pitch 
at a given point B, 3 feet out from the center, we can solve 
the problem graphically by means of the triangle of pitch. 
First we find the circumference described by the given 
point B in one revolution by multiplying the radius by 2 
to find the diameter and then by 3.14; that is, 3 x 2 x 3.14 = 
18.84. We mark this distance on a line C D (Fig. 676) ; from 
one of its ends D draw the perpendicular D E, equal to the 
pitch, and from the other end C, a line C E which joins the 
extreme points of the developed circumference and the 




Fig. 67 



PROPELLERS 93 

pitch. The angle a, formed by the base and the hypotenuse 
of the triangle, is the angle of pitch at the given point B of 
the propeller. 

If, instead, the angle a is known, we find the circumference 
C D, lay the angle on one of its ends C, from this point draw 
an indefinite line C F, inclined at an angle equal to that 
given a, and from the other end D the perpendicular D E. 
The point of intersection E of the two lines determines the 
pitch D E. 

If we want to find the pitch of a propeller in a numerical 
way, given the machine speed, the motor speed and the pro- 
peller slip, the problem is solved in the following way : 

If the data are these: machine speed, 50 M. P. H.; motor 
speed, 1100 R. P. M.; and the propeller slip, 20 per cent; 
we reduce first the miles per hour to feet per hour by multi- 
plying 50 by 5280, then we divide this product by 60 to 
find the feet per minute, and finally we divide this quotient 
by 1100 to find the number of feet in one revolution. This 
last result tells us what the effective pitch of the propeller 
should be to get the speed of 50 M. P. H., and as the slip is 
20 per cent, we must increase accordingly the number found 
to obtain the theoretical pitch of the propeller, so that when 
the slip is deducted, we actually get the necessary effective 
pitch. 

We have then: 

50x5280=264000, 2 -^-° = 4400, gg = 4. 

If the slip is 20 per cent, the efficiency of the propeller is 
80 per cent, and as 4 represents this 80 per cent, we can get 
the theoretical pitch from the following proportion: 

The pitch of the propeller is, therefore, 5 feet. 
Manufacture. — -Propellers may be made of metal or wood. 



94 AVIATION 

Metal propellers have the advantage of cheapness as com- 
pared with wooden propellers, but they have, on the other 
hand, certain drawbacks, which give rise to objection to their 
use. First of all they are heavy, and if they should burst 
under the strain of high velocity, the fragments are apt to 
cause damage. Then they bend easily, and on account of 
their great elasticity they vibrate when in use. Another 
drawback is the quasi impossibility of obtaining an even sur- 
face blade, and finally the difficulty of attaching the blades 
to the propeller arm. 

If a metal propeller is to be used, perhaps aluminum is the 
more suitable to make the surfaces of the blades, because its 
lightness permits of relatively thick blades, which, increasing 
the moment of inertia, preserve their shape. But, all things 
considered, wood propellers are the best, even if they cost 
more. 

Wood propellers are light, and this is their chief charac- 
teristic, from which many a good advantage is derived. 
Being light, they can be made very thick. Their thickness 
makes it possible to shape the blades in a way to offer the 
least resistance to motion, and again to cause an increase 
in the moment of inertia, with a consequent increase in the 
resistance to flexure, which permits, therefore, of a very 
high rate of speed with very little probability of bursting, 
as wood possesses greater tensile strength than the best 
metal, especially with the grain running in the sense of the 
length of the blade; but even if the propeller should burst, 
the fragments being light would not be so dangerous. 

Wood propellers can be made in one single piece or in 
laminations, which are glued together with insoluble glue. 
One-piece propellers are cheaper, but as it is hard to find 
wood of straight grain without any flaws, the laminated pro- 
pellers are to be preferred, because they allow the use of the 
best kind of wood. 

A propeller is usually made with five or six laminations of 
mahogany, walnut or oak. The laminations, besides being 



PROPELLERS 95 

glued together, are held in place by dowels driven through 
them at equal distances. They are held in a press until 
thoroughly dry, then they are cut by machinery into pro- 
peller shape and finished by hand. 

The wood used for a propeller must not be very dry, but 
it must contain a given amount of moisture, which must 
be kept constant, and to this effect the propeller is painted 
with a special filler and then varnished several times. 

Some propellers have metallic protections at the tips and 



Fig. 68 

as the metal can not adhere to the wood, if the machine 
were in flight on a rainy day, the rain would filter through 
and collect at the tip, causing the metal to bulge up and 
tear the propeller to pieces owing to the terrific centrifugal 
force. To avoid this, small holes are bored at the tips of 
the metallic protections to allow the water to run out. 

Balance. — A propeller must be perfectly balanced. There 
are different methods to try a propeller for balance, but the 
best is to mark equal distances from the center to the tip 
on both blades and to weigh the propeller at all the marks; 
for an equal distance from the center, the weight on one 
blade must be equal to that on the other. This is accom- 
plished by inserting one of the tips D (Fig. 68) in a notch 
cut in a wall and hooking the propeller to a spring scale E 



96 



AVIATION 



suspended from a bar F and weighing it at the different 
equidistant marks A, B, C and A', B', C The weight at 
the point of the first mark A on one side of the propeller 
must be equal to that of the first mark A' on the other side; 
the second equal to the second, and so on. 

A slight error in the balance can be corrected by additional 
coatings of varnish on the blade which weighs less or by 
scraping off some of the material near the hub of the blade 
which is heavier. If the difference is too much and can not 
be corrected in this way, the propeller must be rejected. 

Test. — To see if the pitch angle of a propeller is correct, 
it is measured on both blades at equal distances from the 

center by means of a 
protractor or the tri- 
angle of pitch. The 
angles equidistant 
from the center must 
be equal. To accept 
a propeller as good, 
the pitch angle must 
be within ]/2 a de- 
gree of the proper 
angle. 

To test a propeller for warpage, the following method 
may be used : 

Starting from the center A (Fig. 69a) of a propeller B, 
we mark different points C, D and E on one blade; then, 
by means of a protractor, we measure the angle a at the 
inner point C and lay it off at one end A (Fig. 696) of the 
line A B, which represents the developed circumference of 
the circle described by the given point; from the same end A, 
we draw an indefinite line A C, inclined at an angle a equal to 
that measured, and from the other end B, the perpendicular 
B C, which is the pitch of the propeller. The same process 
is repeated for all the other points and if the propeller is not 
warped, the lines which represent the pitch should all be 







PROPELLERS 97 

equal, B C = D E=F G. To facilitate the work, we draw 
the parallel C G from the point of intersection C of the first 
pitch found to the line A B, which represents the developed 
circumference of the first point, and if the blade is correct, 
all the other points fall exactly on this parallel line; but if 
they fall within or without it, the angles are smaller or 
larger than they ought to be and the blade is warped. If, 
instead, it is not warped, the same system is followed to test 
the other blade. 

The length of one blade must be equal to that of the other 
or the difference must fall within 1/16 of an inch to accept 
the propeller as good. 

The width and the camber of the blades must be equal at 
points equally distant from the center. 

An error of 1/8 of an inch is allowed for the straightness 
of a propeller. 

The joints of the laminations must be all perfectly closed 
and the surface very smooth throughout. 

The hub hole and the bolt holes must be perfectly straight 
and at right angles with the face of the hub. 

Care. — A propeller must be kept always in a vertical 
position to protect it from distortion, and the best way is 
to mount it on a wooden peg, which fits the hub hole exactly. 

To prevent the blades from warping, the place where the 
propeller is stored must be neither very damp or very dry, 
nor such as to allow the sun rays to fall on it. If these rules 
are disregarded, the propeller will lose its efficiency and give 
rise to flutter, which will stress the bearings and crank shaft 
of the motor and probably tear it to pieces. 

Boss. — Boss is a metallic device used for the attachment 
of the propeller to the shaft of the motor. 

The simplest form of boss consists of two flanges, one of 
which, A (Fig. 70), is permanently attached to the shaft and 
has eight threaded holes, while the other B is a separate 
piece with plain holes. The propeller C is mounted on the 
shaft between the flanges, which are held together by eight 



98 



AVIATION 



bolts on whose points are also screwed and cotter pinned the 
nuts. While this is the simplest form of boss, it is not the 
best, because the bolts are shaken and 
loosened by the revolution of the pro- 
peller, which is liable to break. 

A good form of propeller boss is that 
used for the Gnome motor (Fig. 71). In 
this case, the flanges are also two A 
and B, but they are both attached to the 
propeller by eight bolts, and one of the 
flanges A has a tubular projection C with 
a keyway D, cut in the inside, in which, 
when the propeller is mounted, fits a key 
E laid in a slot F cut in the shaft, and the propeller is then 
held in place by a nut G screwed on the crank shaft. To 
prevent this nut from unscrewing, a ring spring H is mounted 
on it in such a way that one of its points / goes through one 
of three holes J bored in the nut and inside one of four 
slots K cut on the end of the crank shaft. 




Fig. 70 





Fig. 71 

The Curtiss boss (Fig. 72) is similar to the Gnome, with 
the difference that, beside the eight bolts, there is a nut A 
screwed on the threaded end of the tubular projection to 
help fasten the flanges on the propeller, which is then held 



PROPELLERS 



99 




Fig. 72 



in place on the shaft by screwing on it another nut B. Both 
nuts have three holes for the use of springs, which lock them 
in the slots cut in the tubular pro- 
jection and in the shaft, as in the 
Gnome boss. 

A propeller must be mounted at 
right angles with the shaft. To test 
the alignment, a stick is brought in 
contact with the tip of one blade and 
held in position while the other blade 
is brought around to see if it touches the point of the stick 
as the first blade. If this is not the case, the nuts must be 
tightened on the side of the blade which forms the greater 
angle with the shaft, until the propeller is perfectly aligned. 

As in an aeroplane the motor is cranked by means of the 
propeller, another point to consider in mounting it is to 
put it in such a position that it can be grasped easily and 
the motor started quickly. This means that the propeller 
must be in an inclined position and one of the cylinders of 
the motor on compression, near the firing point. If this is 
not done, it will be very dangerous and hard, if not impos- 
sible, to start the motor. 



CHAPTER V 
MAINTENANCE 

Inspection. — With the exception of the medical profession, 
there is perhaps no other calling in life which has more re- 
sponsibility than that of the aeroplane mechanic: to him is 
entrusted the fate of human beings, who may be dashed to 
instant death through a mere carelessness on his part, and 
there can be no greater remorse than that caused by the 
remembrance of having destroyed human life through lack 
of care. 

To avoid these dire consequences, it is imperative that an 
aeroplane be scrupulously inspected before and after every 
flight, daily and weekly, and maintained in the best condition. 

To inspect a machine before or after a flight, the most 
important parts are looked after, such as the bracing and 
control wires, to see if they are properly tensioned and in 
good condition. The machine must also be cleaned from the 
dust that collects on the wires, which are oiled or greased, 
on the planes and on all the other parts in general. When 
the machine starts from or lands on wet ground, the wheels 
throw off mud on the under side of the wings and it must 
be removed, which is easy to do if the mud is wet, but if 
dry, it must first be dampened, otherwise the fabric may be 
damaged in scraping it off. The motor also throws oil all 
over the machine. If any of it goes on the planes, it must 
be cleaned with gasoline, acetone or hot water and soap. 
When soap is used, it must be of the kind that has no alkali, 
that is, no soda or potash, which damages the fabric. 

In a daily inspection, besides what is done for a flight in- 
spection, all the adjustments of the machine must be looked 
after, to see if the straightness of the wings, the dihedral 
100 



MAINTENANCE 101 

angle, the angle of incidence, the stagger and the controls 
are in perfect order. 

In a weekly inspection, all the parts of the machine, from 
the biggest to the smallest, must be carefully examined, and 
the best way to do this is to have an inspection card with 
all their names written down, to check them off, one after 
the other, as they are examined. 

The wires are first inspected to see that they are not 
damaged, scored, kinked or rusty, and then they are greased 
or oiled. 

The control cables must be inspected thoroughly, espe- 
cially around the pulleys, where the wires are apt to fray. 
If even one only of the small wires is broken, the cable must 
be replaced. As these wires are covered with grease, they 
must be washed with gasoline to facilitate the inspection. 
The control cable connections must also be examined to 
see if they are in perfect order. 

The fittings must be looked after for signs of cracking at 
the corners. 

All the locking arrangements, that is, the safety wires of 
the turnbuckles, the cotter pins and the nuts, must all be 
properly set in place. 

The axle and spokes of the wheels, the rudder post, the 
tail skid post and the struts must be examined for dis torsion 
and replaced if necessary. 

All moving parts, that is, wheels, pulleys, hinges and 
control mechanism must be well lubricated with graphite. 

The shock absorbers of the wheels and tail skid must 
be thoroughly inspected, to see if they have the proper ten- 
sion and if they show any signs of wear. 

The fabric must be examined for wear and tear, and for 
the condition of the dope and varnish. 

It is a good practice to stand some distance away from 
the machine every time it is adjusted, to get used to the 
way it looks and learn to see at a glance its condition, thus 
saving time in the inspection. If, for instance, we stand in 



102 AVIATION 

front of the machine and look at the front struts, when 
they are properly aligned, they must cover the rear ones, 
and if we look at them from the side, the outer struts must 
be in a line with the inner struts. The straightness of the 
wings, both in regard to the leading and trailing edges, can 
be easily detected by looking at them from the front or rear 
of the machine. 

It is well to time every inspection, either partial or gen- 
eral, to know exactly how long it takes and be ready for 
any emergency. 

Forced Landing. — In case of a forced landing in a cross 
country flight, the first thing to do is to choose the proper 
ground to start from at any time, because the weather may 
change suddenly and if the proper spot is not chosen before- 
hand, the start can not be made immediately; then the 
machine must be turned arourid to face the wind and, if 
possible, put under shelter. It is a good plan to dig trenches 
and sink the wheels in them or, if this is not possible, to 
block the wheels to prevent the wind from bbwing the 
machine away. 

If the machine is to remain exposed any length of time 
on a windy day, it is well to picket it by tying ropes from the 
lower part of the interplane struts or the upper part of the 
undercarriage struts to pickets driven in the ground. In 
this case, all points where the cord comes in contact with the 
fabric must be padded with soft material, otherwise the 
rubbing of the cord spoils it. 

The controls must be lashed fast to avoid damage to them 
by being blown about by the wind. 

If the machine is to stay in the open overnight, the pro- 
peller must be covered to protect it from moisture. 

Repairs. — Wood. — The repairs of the wooden parts of an 
aeroplane usually consist in replacing broken members with 
new ones, unless it is an emergency repair in an exceptional 
case, when the highest skill and attention are necessary to 
prevent the collapsing of the part temporarily fixed. 



MAINTENANCE 103 

In substituting a new piece, care should be taken to see 
that it fit exactly, and if there are any holes for the passage 
of bolts, that they be the proper size. If the holes are larger 
than they ought to be, the bolts move and throw the parts 
fixed out of adjustment, and if they are smaller, the intro- 
duction of the bolts may split the wood. 

The washers used for wood must be larger than those 
for metal to give them a greater supporting surface and 
prevent their sinking into the wood. 

Metal. — The fittings are generally made with several 
strips of pressed steel, cut in the proper shape, riveted to- 
gether, brazed and coated with non-rusting paint. If this 
process is not available in making a fitting, the best thing 
is to make it in one piece, cutting the plate accordingly. 
In bending the plate, care must be taken not to form sharp 
corners, as they weaken the metal and cause it to break, and 
as pressed steel has a grain running in one direction only, the 
bends must be made across the grain, otherwise they are weak. 

In substituting an old wire with a new one, it is essential 
to use the proper quality, and to test it, the easiest way is to 
lock in a vise a short piece of it and bend it at a right angle. 
If the wire flattens at the curve, it is too soft; if it roughens, 
that is, shows small cracks at the outside of the bend, it is 
too hard ; and if it does not show any of these two signs, it is 
the right kind to use. 

The solid wires inside of planes must be coated with white 
non-rusting paint, and not with red paint, because any signs 
of rust do not show when covered with red, while they do 
through white, and give a warning. This white paint is also 
more elastic than the red and does not crack with changes 
in temperature. The wires must be dry before being painted, 
otherwise the paint does not adhere, peels off in due time 
and exposes the wires, thus failing to protect them from 
dampness. 

As all wires must be looped to be used, it is necessary to 
know how these loops are made. 



104 



AVIATION 




Fig. 73 



To make the ferrule and loop, the solid wire is inserted in 
a ferrule A (Fig. 73a) and in a shank B, the wire is looped, 

the shank slid in the loop, 
the ferrule slipped back to 
rest against the loop, the 
short length of the wire bent 
over the ferrule and then cut 
off, leaving just a small hook 
to hold the ferrule in place 
(Fig. 736). 
In this process, the follow- 
ing points must be observed: in making the loop, a good 
length of wire must be allowed to be easily bent before cut- 
ting, as solid wire is stiff and can not be bent if it is short; 
and the loop must be oval, well defined, symmetrical, with- 
out scores or angular corners to weaken the wire and cause 
it to break, and of small 
size, otherwise it elongates 
easily under tension and 
throws out of adjustment 
the parts to which it is 
connected. 

If no ferrule is available, 
one may be made by cut- 
ting a short copper tube of 
suitable size and flattening 
it out just enough to make 
it oval. 

The ferrule and loop is 
often dipped in solder to 
fill in the space between 
the ferrule and the wire. 




Fig. 74 



A spliced loop is made by unwinding the strands of a 
wire A (Fig. 74a), making the loop around a thimble B 
(Fig. 746) and inserting one strand at a time in its closed 
strands C by prying them open with a pointed tool. After 



MAINTENANCE 



105 




Fig. 76 



some length has thus been spliced, one wire of each strand 
is cut off and the splicing continued; when another length 
is spliced, another wire is cut off, and so on, until the loop 
is finished. The wires are cut off gradually to taper the 
splicing down towards the end. The splice is served with 
a fine string or a wire D (Fig. 74c) to protect it. 

The thimble and loop is formed by inserting a thimble 
in the loop, winding its ends A (Fig. 75) with fine copper 
wire, skipping a couple 
of spaces B and C 
about 1 / 8 of an inch, 
cutting the end D of 
the wire at a slant to 
taper it down and 
thoroughly soldering 
loop and thimble. 

The wrapped and 
soldered loop requires 
a close winding of copper wire around the part to be 
curved, to prevent the opening of the coils at the outside 
of the bend A (Fig. 76). The remainder of the work is 
done as in the thimble and loop. 

All these loops are fitted with shanks before being closed. 

As the two last loops are soldered, it is necessary to 
know the soldering process to be able to properly finish the 
work. 

Soldering. — For common soft soldering, it is necessary to 
have: solder, flux, blow torch or blow furnace and soldering 
iron. 

The solder is an alloy of tin and lead, usually in equal 
parts, and, therefore, known under the name of "Half and 
half." Sometimes, more tin is used and the solder is then 
harder. 

Flux is a substance that promotes the fusion of metals, 
prevents their oxidation under the action of heat and cleans 
their surface. It may be solid, in paste form or liquid. That 



106 AVIATION 

used for soft soldering is generally chloride of zinc, which is 
formed by dissolving zinc in hydrochloric acid. 

Hydrochloric, or muriatic acid, as it is commonly called, 
is a colorless, corrosive gas, having a sharp penetrating taste 
and suffocating smell. It is exceedingly soluble in water 
and when it comes in contact with the air, it condenses the 
moisture, forming dense, white clouds. 

What is commercially known as hydrochloric acid is a 
strong aqueous solution, colored yellow by impurities, such 
as iron or organic substances. Pure hydrochloric acid is a 
solution of pure gas in distilled water and is colorless. A 
concentrated solution of hydrochloric acid gives off fumes 
when exposed to the air, and when heated, the gas evaporates. 

The commercial acid is obtained in the soda factories by 
pouring strong sulphuric acid on common salt, which gives 
the following reaction: 

2 Na CI + H 2 S 4 = Na 2 S 4 + 2 H CI 
Sodium Sulphuric Sodium Hydrochloric 
chloride acid sulphate acid 

The hydrochloric acid thus given off passes through special 
towers, over whose walls flows a constant current of water, 
which dissolves the gas and collects it at the bottom of the 
towers. 

To prepare the flux, zinc is treated with hydrochloric acid, 
which gives the following reaction: 



Zn 


+ 2 H CI = 


Zn Cl 2 


+ H 2 


frnc 


Hydrochloric 


Zinc 


Hydrogen 




acid 


chloride 





This is known to the trade as "cutting the acid," which 
is considered "raw" before being cut; but, as we see from 
the chemical combination, what really takes place is the 
formation of chloride of zinc, which, if used as flux, prevents 
the oxidation of metals under the action of heat. To add 
to this property of the flux that of cleaning, a few drops of 



MAINTENANCE 



107 



raw acid are poured in it. As the solution must be saturated, 
a greater quantity of zinc is used than that necessary, to 
make sure that there is no more needed, and the surplus is 
removed after the combination ceases, which is indicated by 
the stopping of the bubbling caused by the reaction. The 
acid to be cut must- be poured in an enameled earthen cup, 
as there is development of heat during the combination and 
if a glass vessel were used, it would crack. 

A blow torch is a lamp that burns gasoline mixed with 
air to give a hot, blue flame. Its parts are: a tank A (Fig. 77) 
which contains the gasoline, a 
hand pump B to force and com- 
press the air in the tank, a needle 
C, a needle valve D, a holed 
burner E which mixes the gaso- 
line vapor with the air and gives a 
blue flame, a drip cup F in which 
gasoline is burned to heat the 
burner, a filler plug G to close the 
tank, and a tube H through which 
the gasoline is forced up to the 
needle valve by the air pressure. 

To make the torch ready for use, it is turned upside down, 
the filler plug at the bottom unscrewed and the tank filled 
about % full with clean gasoline. To prevent a leak, it is 
better to first soap the threads of the filler plug and then 
screw it tightly, using a wrench or an iron bar inserted in 
its hole to make sure that the joint is air-tight, but care 
should be exercised not to screw the plug unnecessarily hard, 
otherwise the bottom of the tank will be distorted and 
damaged, being very thin. 

The torch is turned right side up and a good, heavy pres- 
sure of air supplied in the tank by means of the pump. A 
pressure of about 15 pounds is enough for a strong, blue 
flame, but the higher the pressure, the better the flame. If 
the plunger of the_ pump is of the kind that can be screwed 




108 AVIATION 

down, it must be screwed, as it has a needle point on its 
inner end to make a positive shut off. 

The tank is now to be tried for leaks, as a leaky tank not 
only gives a poor flame, but it may also cause a fire on ac- 
count of the gasoline oozing out through the leak and igniting. 
For this purpose, the torch is turned upside down; this 
brings the gasoline to the top part of the tank and in case 
there is a leak, it is easily found and stopped. 

If there is no leak in the tank or fitting, the torch is turned 
right side up and the drip cup filled with gasoline by putting 
one hand against the mouth of the burner and opening the 
needle valve with the other; the gasoline strikes the hand, 
falls in the burner and from there drops in the drip cup. 
When this is full, the needle valve is closed, the gasoline 
lighted and the torch protected from currents of air, so that 
the burner may be thoroughly heated by the flame. Usually 
the amount of gasoline in the drip cup is enough to heat the 
burner properly, but sometimes, especially in cold weather, 
it is not sufficient, and in this case, it is necessary to heat 
the burner by means of a flame (either from another torch 
or a gas flame), as it is impossible to put more gasoline in 
the cup, which, being warm, causes it to vaporize. 

If the tank has been previously tried for leaks and none 
found, then, to fill the drip cup, only a few strokes of the 
pump will suffice to supply enough pressure to force the 
gasoline out slowly, when the needle valve is opened, and 
fill the drip cup without the need of closing the mouth of 
the burner by the hand. Then the full amount of air pressure 
will be supplied to the tank. The drip cup may, of course, 
be filled from a separate source than the tank. 

When the gasoline is nearly burned out of the cup, the 
needle valve is slightly opened and tin jet of gasoline ignites. 
If it does not light from the flame of the cup, it must be lighted 
from the end of the burner and the flame allowed to burn 
in the burner tube as well as in the drip cup. When the 
gasoline is all burned out of the drip cup, the valve is opened 



MAINTENANCE 109 

a little more and the flame allowed to burn low until the 
burner becomes thoroughly heated, then the valve is opened 
enough to give the desired flame. 

A flame about 4 inches long for a quart and 3 inches for 
a pint torch generally gives the best results. 

When through using the torch, the valve must be closed 
only sufficiently to extinguish the flame without using force, 
which enlarges the needle valve and ruins the burner. After 
the flame is out, the valve must be opened again for about 
one-quarter of a turn of the needle. This is done to prevent 
damaging the needle opening, because the heat causes it to 
expand, and when it cools down and contracts, if there is 
not enough room allowed for the contraction, it presses so 
tightly against the needle that it is hard to open and the 
consequent friction spoils the opening, rendering the torch 
useless. 

The principle on which the torch works is this. 

The pressure of air in the tank forces the gasoline out 
through the tube H and the valve D, and, as the jet rushes 
in the hot burner E, it is vaporized and mixed with the air 
sucked in through the holes of the burner by the current 
formed by the jet of gasoline. The mixture of air and gasoline 
gives a hot, blue flame. 

From this, it is clear why the tank must not be filled 
entirely with gasoline, being necessary to leave room for 
the air, so that a high pressure can be brought to bear 
against the surface of the gasoline, because the greater the 
pressure, the more powerful the jet through the burner, the 
greater the suction produced, the better the mixture of air 
and gasoline, and the better the flame. To make sure that 
some air will be in the tank even when it is filled full, its 
bottom is made funnel-shaped, so that, besides facilitating 
the filling, it renders impossible the expulsion of all the air 
from it, although the amount left in is much less than that 
needed. 

If the torch does not work, the tank must be examined 



110 AVIATION 

to see that the filler plug is screwed in tight, that there is the 
proper pressure, the right quantity of gasoline and no leaks. 
If the burner smokes or does not give a blast when the 
tank is tight and the air pressure good, it indicates that the 
burner is dirty or clogged, in which case, it must be taken 
out and cleaned from the carbon formed around it as well 
as in the air holes of the burner. In reassembling, the joints 
must be soaped to prevent leaks. 

If the washer of the filler plug is old or worn out, it must 
be replaced with a new one made of leather or, if leather is 
not available, with a soaped cotton string wound around the 
plug to the right, so that when the plug is screwed in place, 
it will tighten the string. 

The air pump must be oiled often to keep the cup leathers 
soft, as the pump heats in use and the leather dries, causing 
the pump to work badly. A few drops of oil at a time and 
often will keep the pump in good 
condition and increase its life. 

When the torch is not in use, it 
must not be stored in a damp place 
or allowed to remain in contact with 
acid fumes, as it will oxidize. 

The gasoline used for torches should 
Fig. 78 fo Q c i ean anc { kept in clean cans to 

avoid stopping the burner, and it should be of good quality 
to give the best results. 

A furnace (Fig. 78) works on the same principle as a torch, 
but it differs in size, shape and material, being larger, flatter 
and made of iron with a few parts of brass, while the torch 
is mostly brass. 

Although the make of a furnace varies and special instruc- 
tions are furnished by the manufacturers, generally speaking, 
the following rules apply to the majority of them: 

If the burner is rigid, it will, of course, be always in the 
right position, but if it is mounted on a swivel, it must be 
placed in a horizontal position to till the drip cup, and the 




MAINTENANCE 111 

needle opened only enough for the gasoline to fall in the 
cup. 

The swivel action may cause a leak at the shoulder of the 
needle, in which case the stuffing box must be tightened. 

To remove the burner, it is necessary to remove first the 
top chamber by turning the burner so that it stands upright, 
unscrewing the thumbscrew in the center of the chamber 
and lifting it off; then the burner and swivel are unscrewed 
from the standpipe, without taking apart the swivel at the 
union, as not only it is unnecessary, but it may cause a 
leak, if it is not properly reassembled. 

To clean the burner, it must be taken off together with 
the swivel, the spiral core removed and cleaned thoroughly, 
forcing out all dirt from the hole in the center of the 
core by means of a fine wire, and washing the burner in 
gasoline. If the wire strainer cloth at the small end of the 
swivel is dirty, it must be removed and replaced with a new 
one, made of the proper kind of 
strainer cloth, rolled up tightly and 
forced into the hole, to keep out lint M^ 5 

and dirt and save cleaning the burner 
oftener, and also to facilitate the 
vaporization of the gasoline. 

In putting the burner back, care 
must be taken to set it in the proper 
position, so that the gasoline can fill 
the drip cup. 

If there is a leak around the pump collar, caused by the 
washer being old, it must be renewed. 

The so-called soldering iron consists in reality of a quad- 
rangular prism of copper terminating in a pyramid A (Fig. 
79), a wooden handle B and an iron bar C uniting both. 

To prepare the iron for use, it is heated to a temperature 
just short of redness, its sloping end quickly filed bright, 
dipped momentarily into the flux and tinned by rubbing 
it on solder laid on a piece of tin or a hard wooden block. 




112 AVIATION 

The iron may be filed cold or warm, but it is better to file 
it warm, because, in this state, a mere shaking of the iron 
causes the old solder to drop off, and a few quick strokes of 
the file are enough to make the point bright without loss 
of heat. If, instead, it is filed when cold, it takes longer, the 
work is harder, the solder sticks to the file and spoils it, 
and after the iron is heated, it is necessary to file it again to 
remove the oxidation caused by the heat. In reheating the 
iron, after it has lost its proper temperature during the 
soldering process, care should be taken not to heat it quite 
to redness or the solder may burn off, necessitating a repeti- 
tion of the tinning, nor to overheat it to such a temperature 
that the iron burns, and must be filed again, which means 
hard work, loss of metal and time. 

The capital requirement for true soldering is that between 
the metal to be soldered and the solder used there should be 
a certain degree of alloying, an intimate union of the two 
thus taking place. Beside this, it is necessary that the metal 
be bright, clean and free from greasy matter, and that it 
be coated with flux to prevent its oxidation under the action 
of heat. 

When chloride of zinc is used as flux, the metal soldered 
must be thoroughly washed to remove any trace of acid, 
which in due time would corrode it. For this reason, the 
loops that require soldering are dangerous, because the mid 
can not be all removed; but as long as they are still in use, 
it is well to know how to solder them. 

A loop is first coated with flux and soldered on both sides 
with more solder than necessary; then it is laid on a hot 
soldering iron and pulled slowly along it, so that the heat 
melts the solder and causes it to filter through; and finally 
it is thoroughly washed with plain or soaped water. If the 
work is properly done, when the loop is cut, the wire looks 
as if it were solid instead of stranded. 

The openings left in the copper wire winding are for the pur- 
pose of inspection, that is, to see if the solder filtered through. 



MAINTENANCE 



113 



From this process, it is clear that the flux remains inside 
the wire, the surrounding solder making it impossible to 
wash it out, and, consequently, it will exercise its corrosive 
action without being detected until the wire breaks. 

Fabric. — The repairs in the fabric consist in sewing plain 
tears or patching holes. In either case, it is first necessary 
to remove the old dope by rubbing it off with a cloth moist- 
ened with acetone or by applying on it fresh dope and allow- 





ing it to cut the old one, when it is removed by means of a 
piece of cloth. 

A plain tear is sewed with a baseball stitch (Fig. 80a), 
that is, a needle filled with single thread is passed through 
the tear, stuck from underneath in one side A of the torn 
fabric and pulled out, so that the knot remains unseen under 
the fabric, then the needle is inserted again in the cut, stuck 
in the other side B of the cut and pulled out, and so on. 
When the sewing is finished, the thread is cut off and the 
end tucked under -the tear, which is doped, covered with a 
patch large enough to hide it (Fig. 806) and the patch doped 



114 



AVIATION 



also. After this is dry, another patch with frayed edges 
(Fig. 80c) is applied on it and coated with the regular number 
of coats of dope and spar varnish. The last patch is frayed, 
because the frays adhere better than the plain edges. 

To repair a hole (Fig. 81a), it must be filled in with a piece 
of fabric, and to facilitate the work, the hole is cut into a 
regular shape with square corners, which are then slit (Fig. 
816) and the fabric tucked underneath (Fig. 81c) to double 



-6- 



ou 



/ 






it up and make it stronger at the edges, which are to be 
sewed. A piece of fabric is cut of such a size that when its 
edges are tucked under on all sides, it is about 1/16 of an 
inch smaller than the hole all around (Fig. 8 lrf) to make 
possible the stretching of the fabric in sewing it. The corners 
of the fabric are now fixed in place by stitches (Fig. 81e) to 
ascertain that the patch is the proper size and to render 
easier its sewing, which is done with a baseball stitch as 
for a plain tear (Fig. 81/) and the work finished in the same 
way, that is, by doping on it a plain and a frayed patch 
(Fig. 8 If/) and giving the latter the required number of 
coats of dope and spar varnish. 



MAINTENANCE 115 

Rubber. — A puncture in the inner tube of a tire may be 
repaired in an emergency case by means of a prepared patch, 
which is a disk of rubber covered with rubber cement pro- 
tected by a cloth. To make the patch ready for use, the 
cloth is removed, gasoline poured on the cement and the 
patch left in this way for about 15 or 20 minutes. The tube 
around the puncture is washed with gasoline, sandpapered, 
coated with rubber cement and covered with the patch, 
which is held firmly against it by means of a weight until 
it is dry. 

If the puncture is so small that it can not easily be seen, 
the tube is inflated and dipped in water: the bubbles formed 
by the escaping air indicate its location. The tube must, of 
course, be dry before applying the patch, which must be 
handled by the edges to avoid touching the cement with 
fingers soiled with oil or grease and spoiling its adhesive 
property. 

If a steel brush, instead of sandpaper, is used to rub the 
tube, care must be taken to see that the wires are all even, 
as sometimes one of them protrudes more than the others 
and cuts the rubber all over. 

A punctured outer casing or shoe is properly repaired by 
the vulcanizing process, which requires the skillful use of 
special apparatus, but the puncture can be temporarily 
stopped by means of one of the clamps made for this purpose 
and inserted in the casing against the puncture, to prevent 
the inner tube from blowing out through it. As a substitute 
for a clamp, a piece of thick rubber, leather, linoleum or 
anything stiff enough to stop the puncture temporarily may 
be used. 



CHAPTER VI 
FLIGHT HINTS 

Methods of Instruction. — This chapter is not meant to 
teach anybody how to fly — flying "by correspondence" is 
not a possibility — but it simply aims at giving a brief ex- 
planation of how the theory of flight is applied in practice. 

Flying can be learned in three different ways, but in each 
of them a previous thorough knowledge of the elementary 
theory of flight, aeroplane construction and gas engines is 
essential. With this premise, let us examine these three 
different methods. 

A man that owns an aeroplane and has at his disposal a 
good stretch of level, clear ground, suitable for the initial 
runs up and down, may learn slowly and gradually the use 
of the controls before he attempts to leave the ground. This, 
thoroughly accomplished, enables him to make low, short 
jumps which are gradually increased, first to longer and 
longer straight, low flights and then to higher and higher 
altitudes, until he has learned perfectly the use of all the 
controls, so that their manipulation becomes almost in- 
stinctive. Then he can attempt cross country and high 
altitude flights and the performance of all the tricks or stunts 
that go to make the expert aviator. But while this can be 
and has actually been done by the pioneers of aviation, or 
no man would be flying to-day, as no man was born a bird, 
on the other hand, it implies the courting of all the risks and 
dangers, often fatal, encountered by all those who made 
human flight an actual fact. Why, then, take such perilous 
chances when we have to-day plenty of expert instructors, 
who can teach us with the minimum danger? And it is the 
employment of an instructor, coupled with the type of 
116 



FLIGHT HINTS 117 

machine used, which gives us the other two systems of 
learning how to fly. 

If a one-seat machine is used, as was the case before the 
two-seat machine was built, the instructor explains to the 
pupil the manipulation of the controls and mechanical de- 
vices of the motor and makes him execute the different 
motions, first with the machine stationary and then running 
up and down the field, until he has mastered the manipula- 
tion of the controls and motor mechanisms. This instruc- 
tion is followed by the flying lessons, which are first explained 
and practically demonstrated by the instructor and then 
executed by the pupil. From the foregoing, it is easy to 
see that the pupil is always alone in handling the machine, 
and the corrections can be made only after the run on the 
ground or the flight is finished. This, undoubtedly, intro- 
duces an element of danger, which, to be minimized, implies 
a slow, gradual course of instruction with the consequent 
loss of time. While the sponsors of such method admit 
this fault, they claim in its favor the thorough confidence 
gained by the pupil, who, being left upon his own resources 
right from the beginning, will never have any trouble in 
solving his own problems at any time, no matter how hard 
they may be. While there is truth in this, the loss of time 
involved and the ever present source of irreparable injury 
or death certainly do not militate in its favor. 

The quickest, best and, above all, safest method is the 
dual control system; that is, the use of a two-seat machine 
with duplicate controls, which can be used by two persons, 
contemporaneously. This means that the pupil is never 
alone, but has always ready, to keep him out of trouble, 
the helping hand of his instructor, thus eliminating alto- 
gether the possibility of injury, due to faulty handling of 
the machine. The instructor first executes a given maneuver 
and the pupil, having the other set of controls at his dis- 
posal, feels all the motions made by the instructor and learns 
practically how to make them himself; then the instructor 



118 AVIATION 

allows him to repeat the same performance and in case he 
errs, he is instantly corrected, thus learning the proper way 
of handling the controls. Formerly, oral tuition was im- 
possible during flight, due to the roar of the motor, and it 
was given before and after taking the air, but with the in- 
vention of the aerotelephone, even this fault has disappeared, 
and instructor and pupil are now in constant verbal com- 
munication. It is clear that this is by far the best method 
of teaching how to fly, and one which can hardly be improved 
as long as a noisy motor is used to furnish the motive power. 
Still, there are those who object to this system of tuition on 
the ground that it causes lack of confidence in the pupil, 
who, when left alone, doubts his own ability to handle the 
machine and finds himself in trouble, which may bring serious 
consequences. While, admittedly, it is human to become 
nervous in a case like this, on the other hand, the lack of 
confidence in the pupil is due more to the fault of the in- 
structor, and to a certain extent to the pupil's, than to the 
system. If the instructor is really worthy of the name, he 
will not consider himself all the time the master of the situa- 
tion, but will, after he has properly taught his pupil, allow 
him to handle the machine all by himself, being ready to 
come to the rescue only in case of an emergency; in other 
words, the instructor will take the part of a mere passenger 
and allow the pupil to be the pilot. This will increase, rather 
than decrease, the confidence in the pupil, because he will 
attempt all the different maneuvers with the assurance that 
if he goes wrong, no harm will befall him, and thus he will 
acquire a thorough knowledge of practical flying, which he 
will be ready to use at any time afterwards, be he in com- 
pany or alone. If he were, instead, his self-instructor in a 
one-seat machine, would he be better off, would he dare 
execute any of the more difficult feats of daring, which were 
never taught him in a practical way? Evidently, in such a 
case, he has to take a chance, but so did others before him 
and often were maimed or killed. If he is his self -instructor, 



FLIGHT HINTS 119 

he must proceed slowly, gradually, carefully; and this is 
exactly his part with the dual control system when he is 
left alone to fly, if his instructor did not teach him properly. 
Having practically mastered every phase of the evolutions 
through the guidance of the instructor, when the pupil takes 
the air alone, he has to go over one by one all the different 
manipulations, from the easiest to the most difficult, using 
good common sense in everything he does, if he wants to 
become a skillful aviator with the minimum of risk. 

No matter what method used, the course of instruction is 
the same; that is, after having mastered an elementary, 
but thorough knowledge of the theory of flight, aeroplane 
construction and gas engines, the pupil is taught successively: 
taxying or grass cutting, elementary flying, stunts. 

Taxying. — Taxying is the running of an aeroplane on the 
ground, and it has the object of familiarizing the pupil with. 
the manipulation of the controls and motor devices. The 
machine used for taxying is either a heavy one unable to 
leave the ground or a regular machine with the motor so 
adjusted that the power developed is insufficient for flight. 

In the case of the stick control, the manipulations, as we 
already know, are the following: 

The stick pushed down causes the nose of the machine 
to go down; the stick pulled up causes the nose to go up. 

The stick thrown to the right brings down the right side 
of the machine; the stick thrown to the left brings down the 
left side of the machine. 

The foot rudder bar pushed to the right makes the ma- 
chine turn to the right; the foot rudder bar pushed to the 
left makes the machine turn to the left. 

With the wheel control, the only difference consists in 
turning the wheel to the right or left to accomplish the same 
result as when the stick is thrown to the right or left. 

One very important point to impress on the mind of the 
pupil right from the beginning is to hold the control lever 
naturally, without an undue amount of force, and to handle 



120 AVIATION 

it lightly and slowly to acquire the proper touch, and control 
the machine in the right way. The motions of the controls 
during flight are almost imperceptible, especially with a 
very sensitive machine. 

The controls are first operated by the pupil while the 
machine is stationary and then the manipulations are re- 
peated with the machine in motion on the ground under its 
own power. Usually, the machine runs in a straight line 
from one end of the aviation field to the other, then the 
motor is throttled down or stopped and the machine turned 
around by hand to repeat the run; but sometimes the turn 
is made under power by manipulating the controls accord- 
ingly. 

There is quite a difference between handling a machine 
on the ground and in the air: on the ground, there is to take 
into consideration the friction of the wheels and skid against 
the surface of the earth, which, especially in a badly made 
turn when the machine is under power, may cause the 
stripping of the tires, the buckling up of the wheels or the 
smashing of the undercarriage. There is also the possibility 
of breaking the wings by too steep a bank, which causes the 
wing tips to come in contact with the ground. 

When the pupil becomes proficient in handling the con- 
trols, he is taken up in the air in a dual control machine and 
instructed in the art of flying. 

Elementary Flying. — Here is the proper time to point out 
something really bad, which is possible only with the dual 
control method of instruction and which once more goes to 
show that it is not the system that is wrong, but the instruc- 
tor — sometimes. 

There are so-called expert instructors — and they may 
really be experts in aviation, but not by any means in psy- 
chology — who take an immense delight in frightening to 
the highest degree the poor pupil they take up for the first 
time. That this is a pernicious habit, which ought to be 
stopped or punished, if possible, is not necessary to empha- 



FLIGHT HINTS 121 

size, but it is well to say that such a mischievous trick has 
sometimes had terrible consequences, which by themselves 
ought to be sufficient to warn the would-be silly teaser. In 
one particular instance, an instructor, who was taking up a 
pupil for his first flight, aimed the machine straight for a 
hangar, expecting to jump over it within the least distance — 
an easy thing to do for an expert aviator — but the pupil, 
thinking the instructor had gone crazy, unexpectedly took a 
hand in the matter and, frightened as he was, operated the 
controls with such a jerk that the aviator was unable to 
execute the necessary maneuver instantly and the machine 
went to smash itself against the hangar. This was the re- 
sult of a mean trick on the part of a man, whose duty was 
just the opposite. But flying is safe if properly done, and 
a great deal in the improvement of the aeroplane is due to 
the war, which, horrible as it has been in all other respects, 
has given a great impetus to aviation, on account of the 
millions spent in perfecting the aeroplane as an engine of war. 

For instruction purposes, when a single-seat machine is 
used, the best suited is the inherently stable; but with the 
dual control, it is better to use a machine with rather high 
power and sensitive controls. 

In teaching his pupil, the instructor first executes himself 
the simplest manipulations and then tells the pupil to repeat 
them, correcting and advising him constantly with his viva 
voce instructions. 

An instructor may, for instance, proceed by having the 
pupil perform the different maneuvers in the following order: 

Straight flight. This will teach the pupil to hold the 
controls in the neutral position and experience the impossi- 
bility of keeping the machine level and on a straight course, 
due to the constantly changing currents of air, without the 
continuous manipulation of the controls. 

Slight deviations from the straight course by pushing the 
rudder first to the left, which is easier of accomplishment, and 
then to the right, so that he may get used to turn both ways. 



122 AVIATION 

Slight climbs and descents to get used to the manipula- 
tion of the elevators. 

Slight sideways motions to learn how to operate the ail- 
erons. 

Steeper climbs and descents. 

Sharp left and right turns separately, involving the con- 
temporaneous use of rudder and ailerons, as the machine 
must be banked in a sharp turn to prevent side slipping or 
skidding. 

Left and right, right and left turns combined so as to 
describe a figure 8. 

Slight climbing turns to combine the use of all the controls. 

Gliding with motor throttled down and with the motor 
stopped. 

Spiraling, or gliding and turning in the meantime in 
smaller and smaller circles with the power shut off. 

Ascending from the ground. 

Landing against the wind and across the wind. 

Notice that landing is at the bottom of the list, being the 
most difficult thing to learn, while ascending immediately 
precedes it, as it is easier than landing, but harder than any 
aerial maneuver. 

For each evolution in the air, the instructor teaches the 
pupil how to recover from it and bring the machine back 
to the normal position. 

When the pupil can handle the machine perfectly well, 
without the presence of the instructor, — solo flying — then 
he will be taught advanced flying, which will classify him as 
an expert aviator. 

Stunts. — The capital requirements of a stunting machine 
are strength and sensitiveness of controls. Of course, some 
of the stunts can be made with relatively slow and not very 
strong machines, but, on all occasions, it is better to remem- 
ber the wise golden rule: Safety first! 

Before proceeding to explain some of the most common 
stunts, it is well to go over a few things already treated, to 



FLIGHT HINTS 



123 



add and explain a couple of new terms and different func- 
tions of the controls. 

The heavier and slower a machine, the less sensitive the 
controls. 

Even in a speedy machine, the controls become less effi- 
cient if the speed slackens; the efficiency of the controls is, 
therefore, directly proportional to the speed. 

As all water machines are heavier and slower than land 
machines, it follows 
that the manipulation 
of the controls differs, 
being more pronounced 
in the former than in 
the latter. 

In order to execute 
stunts safely, especi- 
sl\y for the beginner, 
it is necessary to at- 
tain a good altitude, 
because whenever the 
machine is not in its 





B 


£ 



Fig. 82 



normal, level, straight flight, there is loss of lift with a con- 
sequent sagging effect. 

It is necessary to remember how the absence of the pro- 
peller torque, when the motor is stopped, affects a single- 
propeller machine, whether it has or not wash in or wash out. 

In case of a very steep or vertical bank, the functions of 
rudder and elevators are completely reversed: the rudder 
A (Fig. 82) being then in a horizontal position will be used 
to bring the nose of the machine up or down; the elevators B 
being vertical serve to make the machine turn around. 

In connection with steep banks, the terms used for the 
rudder are: top rudder and bottom rudder, irrespective of 
the fact that in either case it may be right or left rudder. 
For instance, if the- machine is banked so that the right wing 
A (Fig. 83a) is down, then bottom rudder B, in this case, 



124 



AVIATION 



would be equivalent to right rudder; but if the case is re- 
versed, that is, if the machine is banked with the left wing 




x 




Fig. 83 

C (Fig. 83) down, then bottom rudder D would mean left 
rudder. 

If we first consider a machine in its normal flying position 




Fig. 84 

(Fig. 84a), but with the wings banked, and then we consider 
it upside down (Fig. 84) and with the same bank, what 



FLIGHT HINTS 



125 



in the first case is considered as the lower wing A and the 
higher wing B, in the second becomes higher A' and lower B' '. 
The bank is corrected in both cases with the same manipula- 
tion of the controls, the difference being that in the first case 
the wing would be depressed, while in the second it would 
be raised. 

The above facts must be taken into consideration 





Fig. 85 

whenever handling a machine either in regular flight or 
in stunts. 

Now, let us take up some of the principal stunts. 

Side slip (Fig. 85) is the sideways fall of an aeroplane due 
to over banking. 

To side slip: bank steeply. 

To recover from a side slip : move the control lever forward, 
throw lever towards the higher side of the machine until it is 



126 



AVIATION 



level, neutralize the lever, pull the lever back gradually to 
flatten the course of the machine, neutralize the lever. 




Fig. 86 

Spin (Fig. 86) is a sideways whirling fall of an aeroplane 
due to underbanking in a turning motion. This gives us 



FLIGHT HINTS 



127 



the clue how to reproduce it voluntarily, but there is this 
important point to remember: when a spin is involuntary, 




Fig. 87 

the motor may or may not be running, and in case it is, it is 
wise to throttle it down to avoid undue speed and consequent 



i 




128 



FLIGHT HINTS 129 

stresses, while to reproduce a spin voluntarily, the first 
thing to do is to throttle down the motor. 

To make a spin: throttle down the motor, put the rudder 
on sharply, pull back the control lever. 

To recover from a voluntary or involuntary spin : neutral- 
ize the rudder, push down the control lever, pull back the 
lever gradually to flatten the course of the machine, neutral- 
ize the lever. 

Tail slide (Fig. 87) is the falling of an aeroplane tail fore- 
most, caused by a climb up to the stalling angle. 

To produce a tail slide: pull the control lever back and 
climb steeply until the machine stalls, throttle down the 
motor. The machine falls tail foremost at first, but then 
the nose drops gradually and a dive begins. 

To recover from a tail slide : pull back the lever gradually 
when the machine begins to dive in order to flatten its course, 
throttle on the motor. 

Loop (Fig. 88) is a circle described by an aeroplane through 
the proper manipulation of the elevators. 

The elevators must be operated properly to avoid a stall, 
and they must be assisted by the rudder and ailerons to keep 
the machine on a straight, level course to prevent a side 
slip, and by the timely throttling down of the motor to 
avoid a tail slide or too wide a loop. 

To loop: climb at a good altitude, dive, pull back the 
control lever gradually until the machine is in a vertical 
position, pull the lever all the way back, throttle down the 
motor at the top of the loop, push down the lever just short 
of the neutral position as the machine begins to fall nose 
first, pull the lever gradually until the machine flattens out, 
throttle on the motor. 

If a second loop is to be made, then the course of the ma- 
chine is not flattened out at the end of the first loop, but it is 
allowed to dive until it acquires the necessary speed to repeat 
the looping evolution. 




o 

SI 




FLIGHT HINTS 131 

Roll (Fig. 89) is the turning motion of an aeroplane around 
its longitudinal axis. 

If the machine is to turn around its longitudinal axis, 
it is clear that this operation must be brought about by 
means of the ailerons. If the machine is banked and kept 
banked with the motor running, the continued operation of 
the ailerons will cause it to turn over and over, thus producing 
a screw-like action, which assists the forward motion, but as 
there is loss of lift, which tends to make the machine sag, 
it is necessary to aid this evolution by the occasional use of 
the rudder and elevators. 

To make a complete left roll, the operation may be sum- 
marized thus: push down the control lever and then pull 
it up so that the machine first dives and then climbs, bank 
sharply until vertical, put on bottom rudder to assist the 
rolling motion, neutralize the rudder, pull back the lever to 
lower the nose a little when the machine is upside down, put 
on top rudder when the machine is again vertical, neutralize 
the rudder when the machine returns to its normal position. 

This completes the roll. If more consecutive rolls are 
desired, the operation is repeated over and over. 

The process to be followed to obtain a complete right roll 
differs only in the operation of the rudder, which, instead of 
being first bottom and then top rudder as in the present 
case, will be reversed : top and bottom rudder. 



APPENDIX 
AERODYNAMICAL FORMULA AND CALCULATIONS* 

My study of aeronautical science, or rather my battle with the 
text-books on aerodynamics, has been the longest, hardest mental 
struggle of my life. 

Contrary to the rule for the mastery of knowledge, the more I 
studied, the less I knew; but, luckily, the less I knew, the more grew 
my desire to know. And I studied all the aeronautical books I could 
get hold of and written in the languages I understand, but the 
result was simply the twentieth-century reestablishment of the 
ancient kingdom of Babylonia right between my brains, and an 
infernal dance of angles, sines, cosines, tangents and coefficients, 
which brought about such a tremendous pressure against the 
center of gravity of my brain as to threaten to unbalance it and 
to render myself fit for a straight flight right into an insane asylum. 
And this would certainly have been 'my fate, if a great scientist 
did not, unknowingly, come to my help. 

This great scientist is the illustrious brother of our illustrious 
President, Sir Hiram Maxim. 

In his valuable book, "Artificial and Natural Flight,' ' I found 
the solution of the hard problem; not only for its sound teachings, 
but, also, for its emphatic approval of another book, which I had 
already studied and which, as all others, I was in doubt to follow, 
until so high an authority recommended it as "the most elaborate 
and by far the most reliable." 

One thing that attracted my special attention in studying Sir 
Maxim's book was the fact that, in my trouble in regard to the study 
of aerodynamics, I was in good company, as he himself had 
the same experience when he first started to learn this famous 
science. 

And not to alter the peculiar Maximian style, I will quote his 
own words. 

* Lecture delivered before the Aeronautical Society of New York 
in February, 1911. 

133 



134 APPENDIX 

"During the last few years, a considerable number of text-books 
have been published. These have for the most part been prepared 
by professional mathematicians, who have led themselves to be- 
lieve that all problems connected with mundane life are susceptible 
of solution by the use of mathematical formulae, providing, of course, 
that the number of characters employed are numerous enough. 
When the Arabic alphabet used in the English language is not 
sufficient, they exhaust the Greek also, and it even appears that 
both of these have to be supplemented sometimes by the use of 
Chinese characters. As this latter supply is unlimited, it is evi- 
dently a move in the right direction. Quite true, many of the 
factors in the problems with which they have to deal are completely 
unknown and unknowable; still they do not hesitate to work out a 
complete solution without the aid of any experimental data at all. 
If the result of their calculations should not agree with facts, 'bad 
luck to the facts.'" 

In another part of his book he says further, 

"Some of the mathematicians have demonstrated by formula?, 
unsupported by facts, that there is a considerable amount of skin 
friction to be considered, but as no two agree on this or any other 
subject, some not agreeing to-day with what they wrote a year ago, 
I think we might put down all of their results, add them together, 
and then divide by the number of mathematicians, and thus find 
the average coefficient of error." 

But let us consider this controversy as a thing of the past, and 
and let us follow Sir Maxim's teachings and recommendations, 
which favor the use of Ritter von Loessel's formula?. 

The most important law governing aerial flight is based on the 
resistance of the air against a plane moving through it; and while 
all scientitsts agree that this resistance is proportional to the sur- 
face of the plane and to the square of its velocity, no two agree on 
the value of the coefficient of resistance, which has been baptized K. 

This famous or infamous coefficient K, as a French writer calls 
it, or this ghost, as a member of our Society most appropriately 
named it, has been made to assume values ranging from 55 to 132 
grammes to the square meter, which, as you see, shows very little 
difference. Anyhow, according to the latest edition and from 
experiments made on the Eiffel Tower, the value of the coefficient 
K is made equal to 80 grammes per square meter. So, barring 



APPENDIX 135 

further editions and extras, we can take it for granted that we know 
the value of the coefficient of air resistance. 

Now, then, if we call R the resistance of calm air against a plane 
moving perpendicularly through it, S the surface of the plane ex- 
pressed in square meters, and V its velocity in meters per second, 
we obtain the formula: 

R = KSV* 

I said calm air, because if the air has a motion of its own, v, then 
the formula will be : 

R = KS(V=±v)* 

And it will be +v if the air moves in the sense of the motion of the 
plane, — v if in opposite sense, and Ov if in calm air. 

We will consider only this last case. 

This, therefore, gives us the resistance of the air against a plane 
moving perpendicularly through it, but in this way we could not 
obtain sustentation, as the plane simply meets the air squarely in 
front of it and uses up all its energy in forcing it back, without pro- 
ducing useful work. What we need, instead, is that the plane be 
placed in such a position that the air give up some of its energy 
to the plane. Evidently, to produce this effect, we must place 
the plane in an inclined position, so that the air, meeting it at the 
forward edge, instead of being forced back, is compelled to flow 
away at the rear, producing useful work. 

And here we are again up against another controversy, which 
rivals in importance that of the coefficient K; that is, the determina- 
tion of the resistance of the air against an inclined plane, according 
to its angle of incidence. 

Without losing time in discussing Newton's formula, and the 
opinions given in favor and against it by aero-mathematicians of 
the present day, we will use von Loessel's formula, which gives the 
resistance of the air against an inclined plane, moving through it, 
as being proportional to the sine of the angle of incidence. We will 
have, then, the formula: 

Ra = K S F 2 sina 

in which a is the angle of incidence. 

Let us consider, now, the plane A B, moving through the air at 
an angle ABC. 



136 



APPENDIX 



The air will exercise against the plane a certain resistance R, 
which we will consider as resolved in two forces: R' and R"; the 




90 

first, R', tending to lift the plane, and the second, R", resisting the 
forward motion. 

The vertical component R' is the lift of the surface, and the hori- 
zontal component R" is the drift. 

The center of pressure of a plane surface is near the front at 0° 
of incidence, and it travels slowly backward as the angle increases, 
until it reaches the middle of the surface at 90°. 

The formula which will enable us to find the center of pressure 
of a plane surface moving through the air at different angles of 
incidence is: 

X = (0.2+0.3 sin a) I 

in which I is the length of the inclined side. 
If we make 1=1, the formula will be: 



If sin a = 0, 
and if sin a= 1, 



z = 0.2+0.3 sin a 
z = 0.2+0.3X0 = 0.2, 
£ = 0.2+0.3X1 = 0.5. 



At 0°, then, the sine being O, we find that the center of pressure 
is at 2/10 from the front edge; and at 90° the sine being 1, the 
center of pressure is at 5/10 from the front edge; that is, at the 
center of figure, and, therefore, the center of figure and the center 
of pressure coincide. 



FLIGHT HINTS 137 

Calling L the lift and D the drift, we may resolve the formula: 
Ra = KS F 2 sina 
into the two components: 

L = K S V 2 sin a cos a 
D = KSV*sm*a 

Sir Maxim uses different and practical methods to find out 
the lift and drift, but his considerations agree perfectly with von 
Loessel's formulae. 

Sir Maxim says that "the lifting effect will be just as much 
greater than the drift, as the width of the plane is greater than the 
elevation of the front edge above the horizontal." But he admits 
that "as the front edge A of the plane A B is raised (A') its pro- 




91 

jected horizontal area B C is reduced (B C), and that if we consider 
the width of the plane as a radius, the elevation of the front edge 
will reduce its projected horizontal area just in the proportion that 
the versed sine C D is increased (CD). But, as for the sharpest 
practical angle of flight this reduction is about 2 per cent, while for 
the lower and more practical angles the reduction is considerably 
less than 1 per cent, this factor is so small that it may not be 
considered at all in practical flight." 

Now, as in von Loessel's formulae the lift is proportional to the 
product of the sine and cosine of the angle of incidence, and this 
product is a little smaller than the sine of the same angle, and the 
difference increases as the angle increases, we see that the small 
factor mentioned by Sir Maxim is taken into consideration by von 
Loessel, and the formula generalized for all angles. 

This careful study of details by von Loessel explains the reason 
why Sir Maxim so highly commends his work. 

Evidently, the lift is the weight that can be raised by the plane, 



138 APPENDIX 

and the drift the resistance that must be overcome to obtain 
forward motion. If we, therefore, call W the weight of the plane 
and substitute it for L in the formula giving the lift, we will 
have: 

W = K S V 2 sin a cos a 

And if we want to express the drift in H P, we will obtain the fol- 
lowing formula: 

HP = KSV* sin* a 
75 

because the formula of the drift, 

D = KSV 2 sin* a 

gives us the drift in kilograms and to express it in H P, we must 
multiply it by the velocity, V, and divide by 75, as 75 kilogram- 
meters make one H . P. 

By dividing the L or W by the H P, we will obtain the lift or 
weight per H P, that is, 

W K S V 2 sin a cos a _ K S V 2 sin a cos a 75 cos a 75 _ 
HP = K S V" sin* a = K S F 3 sin 2 a = V sin a ~ 
75 
_ 75 cos a 75sin a 75 _ 75 

V sin a V cos a V V tg a 

The formula giving the lift and the formula of the drift expressed 
in H P enable us to calculate any one of the elements entering in 
the consideration of horizontal flight, when we assume as known 
the other elements. But these formulae are not final. Other and 
important considerations will modify them. 

So far, we have been figuring on plane surfaces, but it is a well- 
known fact that arched surfaces possess greater lifting power, for 
the same amount of energy used, than plane ones. We must, 
therefore, know the coefficient of resistance of the arched surfaces, 
and multiply by it the value given by our formulae. As this co- 
efficient is not constant, but varies with the arching of the surface, 
we must determine it for the special form we want to use, and 
apply the value found to the formulae giving the lift and drift. If 



APPENDIX 139 

we call C this coefficient of curvature, our formulae will become: 

W = C K S V 2 sin a cos a 
C KSV* sin* a 



HP =■ 



75 



in which C is greater than 1. 

Another consideration, which may be made to further alter these 
formulae, is the knowledge that the area of the plane, found by- 
multiplying its dimensions, is not really the effective area; that is, 
considering the actual surface area, we get less lifting power than 
we ought to. A plane one meter square will not lift one-tenth as 
much as one that is one meter wide and ten meters long. This is 
because the air slips off at the ends. In designing planes, therefore, 
we must not forget that area alone is not sufficient. The plane 
must have a certain length of entering edge in proportion to its 
width. 

But although we know this to be a fact, no formula seems to be 
reliable enough at the present day to deserve any serious consid- 
eration. We can, therefore, do away with them all, and leave the 
formulae as they are. 

Let us consider, now, the formula giving the H P. 

This formula gives us the means to determine the theoretical 
resistance to the forward motion of the plane. But in practice 
we know that using a motor of a given H P to drive a propeller 
in order to obtain this forward motion, the propeller does not de- 
liver all of the power transmitted by the motor, but only a certain 
percentage, according to the efficiency of the propeller used. The 
theoretical power, then, given by our formula, is cut down ac- 
cordingly. 

E 
If we call the efficiency of the propeller, we will have to 

multiply by it the theoretical power given by our formula, and 
we will have, then: 

75 100 

Or, if we want to know what must be the H P of the motor to use, 
so that, when reduced by the slip of the propeller, it will give us 



140 APPENDIX 

the actual power required to drive our plane, we must divide the 
theoretical power by the efficiency of the propeller, and in this 
case the formula will be: 

. _ _ C KSV* sin 2 a E C K S V* sin 2 a 100 

A H P = : — = x — 

75 100 75 E 

But this is not all. Besides the loss through the slip of the pro- 
peller, we have to consider the head resistance of the framework 
of a flying machine, motor and aviator. And this is by no means 
a matter of little importance or easy calculation. It all depends 
on the shape, cross section and inclination of the different parts 
used in building the machine. It is, therefore, impossible to give 
specific rules for the computation of the head resistance. All we 
can say is that it must be calculated separately for every machine, 
and that to be reduced to the least, we must avoid plane surfaces 
perpendicular to the direction of motion of a flying machine, and 
use in the construction of the framework those shapes best cal- 
culated to reduce head resistance. For each shape and cross sec- 
tion of bar, there is a special coefficient, which must be applied for 
each special case. Round bars, for instance, or oval, bipointed 
bars, set with one of the points to the direction of motion, offer 
less resistance than others differently shaped. 

Anyhow, whatever this head resistance may be, the power neces- 
sary to overcome it must be found out and added to that already 
calculated, and in this way we will get the sum total of the actual 
power required to obtain horizontal flight. 

In other words, after we have calculated the theoretical power 
required to drive our plane through the air, we must find out the 
loss of power through the propeller slip and head resistance, and 
increase accordingly the H P required. 

If we suppose to have calculated the surface area of the head 
resistance, Sh, and consider it as a plane surface moving perpen- 
dicularly in the direction of motion of the flying machine, we will 
have the formula: 

Rh =KS h V> 
or expressed in H P: 

K Sh V 3 



APPENDIX 141 

which must be added to the actual H P found before, that is, 
C K S F 3 sin 2 a 100 



A HP 



75 E 



to obtain the total H P required to accomplish horizontal flight, 
so that the total H P will be: 

CKSV*sm*a 100 KS h V* 
75 E 75 

Considering the expression of the formulae giving the drift and 
lift, we see that the drift increases as the square of the sine of the 
angle of incidence, and the lift increases as the product of the sine 
and cosine. This last product is a maximum when the angle is 
45°, but taking into account the drift, we find that the best lift 
drift ratio is really attained for angles smaller than 45°. At 45°, 
as sin = cos, sin X cos = sin 2 , and, therefore, L = D. 

As the practical angles of flight are small, it follows that the drift 
is much smaller than the lift; and as the lift is in reality the weight 
of the aeroplane, or, in other words, the force of gravity, we see 
that the power required to raise an aeroplane is much smaller than 
the force of gravity. The aeroplane, therefore, is very economical 
in regard to power, compared with the helicopter or ornithopter, 
as these machines, to leave the ground, must produce first of all 
a vertical force powerful enough to overcome that of gravity, and 
this without considering the power lost in consequence of the ex- 
treme fluidity of the air. 

Sir Maxim in this regard says: 

"Recently there has been a great deal of discussion regarding the 
comparative merits of the aeroplane system and the helicopter. 
Some condemn both systems and pin their faith to flapping wings. 
It has been contended that the screw propeller is extremely wasteful 
in energy, and that in all nature neither fish nor bird propels itself 
by means of a screw. As we do not find a screw in nature, why 
then should we employ it in a machine for performing artificial 
flight? Why not stick to nature? In reply to this, I would say 
that even nature has her limits, beyond which she cannot go. 
When a boy was told that everything was possible with God, he 
asked: ' Could God make a two-year old calf in five minutes?' 
He was told that God certainly could. 'But,' said the boy 'would 



142 APPENDIX 

the calf be two years old? ' It appears to me that there is nothing 
in nature which is more efficient, or gets a better grip on the water 
than a well-made screw propeller, and no doubt there would have 
been fish with screw propellers, provided that Dame Nature could 
have made an animal in two pieces. It is very evident that no 
living creature could be made in two pieces, and two pieces are 
necessary if one part is stationary and the other revolves ; however, 
the tail and fins very often approximate to the action of the pro- 
peller blades; they turn first to the right and then to the left, pro- 
ducing a sculling effect which is practically the same. This argu- 
ment might also be used against locomotives. In all nature, we 
do not find an animal traveling on wheels, but it is quite possible 
that a locomotive might be made that would walk on legs at the 
rate of two or three miles per hour. But locomotives with wheels 
are able to travel at least three times as fast as the fleetest animal 
with legs, and to continue doing so for many hours at a time, even 
when attached to a very heavy load. In order to build a flying 
machine with flapping wings, to exactly imitate birds, a very com- 
plicated system of levers, cams, cranks, etc., would have to be 
employed and these of themselves would weigh more than the 
wings would be able to lift." 

In order to apply to a practical case the formulae given, let us 
suppose that we want to build an aeroplane. 

We must assume the knowledge of some of the values of the 
formulae to calculate the other values. 

In the formula giving the lift: 

W = C K S 7 2 sin a cos a 

we know only the value of the coefficient K, and we may know 
that of C, if we give to our planes a curvature whose coefficient is 
known, otherwise we have to find it out practically ourselves. Sup- 
posing, then, that we have the value of C, we need to know at least 
three more values, before we can determine the fourth. 

Now, we usually know the weight of our machine and the angle 
of incidence, which we choose as best; what we must determine, 
therefore, is either the surface, to find out the velocity, or the 
velocity, to figure out the surface. 

It is up to us, then, to set out the value of the one or the other, 
according to our own wish in regard to the speed of the machine. 



APPENDIX 143 

If we increase the speed, we diminish the surface, and vice versa. 
But, of course, this is by no means arbitrary, and we must have 
an idea right from the beginning, of what we want, otherwise we 
will get the data of a machine which theoretically fulfills our wants, 
but practically is an impossibility. 

If we started to figure out the weight of the machine, we must 
have considered its dimensions in regard to its approximate sur- 
face, so as not to compel us at the end to alter completely its di- 
mensions and consequently its weight. So it is, too, in regard to 
the velocity and load, as we must figure on the strength of the 
material in regard to the stress that the framework can stand with- 
out a breakdown. The same rule holds in regard to the proportion 
of the weight to the power of the motor. 

If we have started without an approximately correct idea of what 
our machine is going to be, we might find out at the end that either 
the surface is too small, or the machine is too weak, or the motor 
is too heavy for the power it gives. 

In this case, we would be in the same position of the early ex- 
perimenters, who had to spend years before they could find out 
the proper data to build a successful machine. 

The best thing to do, then, is to study the approved types of 
existing machines, and vary their proportions according to our 
special case. 

Anyhow, more than one calculation is always necessary to 
vary our erroneous assumptions, before we get the final correct 
result. 

Let us see, now, how from our fundamental formula giving the 
W, we can derive the value of all the other unknown quantities 
in it contained. 

From the formula: 



we have: 



w - 


= CKSV 


2 sin a cos a 


s 




W 


CKV 2 


sin a cos a 


V = 




W 


yC K S sin a cos a 




a cos a = 


W 


sin 


C KSV* 



144 APPENDIX 

For the last formula, as we have no tables giving the product 
of sines by cosines, we will have to use the knowledge that the sine 
by the cosine of an angle is equal to one-half the sine of an angle 
double. Therefore, after we find the product sin by cos, we have 
to double it, to know the sine of the angle double; then we find, 
in the tables of the natural functions of angles, which angle in 
degrees corresponds to this sine, and we divide the degree by two, 
to arrive at the angle we are looking for. For this reason, the 
formula may be expressed: 

2TT 



sin 2a 



C KSV* 



and, if found convenient, the same substitution may be made in 
all the other formulae. 

Suppose, now, that for our machine we want to use a 30 H. P. 
motor weighing 65 Kgs., that the plane surface is 25 square meters 
and inclined at an angle of 7°, that the framework weighs 125 Kgs. 
according to our calculations in regard to the strength of the ma- 
terial chosen, that the coefficient of curvature is 1.25, and, finally, 
that the aviator weighs 60 Kgs. The total weight of the machine 
will be, then: 65 + 125 + 60 = 250 Kgs. 

Knowing the weight, the surface and the angle of incidence, we 
can find the velocity from the formula: 



"V, 



W 



C K S sin a cos a 

as we have all the numeric values of the quantities which deter- 
mine the value of V; that is, W = 250, C = 1.25, K = 0.0S0, 
S = 25, sin angle 7° = 0.1219 and cos angle 7° = 0.9925. There- 
fore: 



V-J- 

V u 



250 =28 



25 X 0.080 X 25 X 0.1219 X 0.9925 

The velocity of our aeroplane will be, then, 28 meters per second. 
Found the value of V, we can find the H P, that is : 



„ D CKSV*am*a 1.25x0.080x25x283x0.12192 inoo 
75 75 



APPENDIX 145 

Supposing that the efficiency of the propeller we want to use is 

80 

— , the actual H P will be: 
100 

AH P = 10.82 X — = 13.52 
80 

If we consider the surface area of the head resistance as equiva- 
lent to a plane of 0.50 square meters moving orthogonally through 
the air, then: 

Rh= K8 h V != 0.080 X 0.50 X^ = 

75 75 

Attention should be paid to the fact that only one-half square 
meter of surface of head resistance requires about as much power 
as 25 square meters, or 50 times as much surface, set at the angle 
of 7°. This tells clearly the enormous power required to drive the 
framework alone of the machine. 

The total H P will be, therefore: 

T H P = 13.52 + 11.70 = 25.22 

As our motor is 30 H P, we have a good margin left, and, con- 
sequently, the machine will fly. 

And now that our aeroplane is ready to take the air, let me jump 
in and fly away.* 

* The formula giving the T H P could be simplified into 

_ „ _ K V 3 (100 C S sin 2 a + Sh E) 

j. H. P = — — 

75 E 

but it was not, in order to show all the different data entering in the 
final calculation. 

The aerodynamical formulae given in the metric system may be re- 
duced in British units by making: K = 0.003, S = area in square feet, 
V = velocity in miles per hour, W = pounds and H P= 33,000 foot 
pounds per minute. Thus, the formulae visibly changed would be 
those in which enters the computation of the horsepower, that is, 
KSV* sin* a 
33,000 
and following; the others remaining the same algebraically and differing 
arithmetically only relatively, according to the values substituted for 
the letters in the application of either the metric or the British system 
of measurement, but being the same in absolute value. 



DEFINITIONS 

Acetone is a limpid, colorless, volatile liquid of penetrating 
ethereal odor and pungent taste, obtained from the products of 
the destructive distillation of wood or by heating calcium acetate. 
It is a useful solvent for gums, resins and fats. 

Aerodrome is the ground used for the practice of aviation. 

Aeroplane is a power-driven aircraft sustained in flight by the 
reaction of the air against wings set at an angle with the line of 
motion. It is distinguished as monoplane and multiplane, accord- 
ing to the number of superposed wings used; the biplane, triplane, 
etc., being particular cases of the multiplane. 

Aileron is a controlling plane hinged horizontally to the rear of 
a wing toward the tip and used for lateral control. 

Air speed meter is an instrument which measures the velocity 
of the air and, as a consequence, that of an aeroplane when installed 
on it. 

Algebra is the science of numbers expressed by letters and 
symbols. 

Equation is the expression of the condition of equality between 
two algebraic quantities or set of quantities, the sign = being 
placed between them. 

Formula is a rule or principle expressed in algebraic lan- 
guage. 

From the above definitions, it follows that the aerodynamical 
formulae are equations. What we want to know, then, is how to 
solve an equation, in order to find out the values of the different 
quantities expressed by the letters of the formulae. 

In arithmetic, we express quantities by means of numbers; in 
algebra, we use letters, which give us a better opportunity to gen- 
eralize a given rule. Suppose, for instance, that we want to express 
in a general way how to find the surface area of a rectangle. Geom- 
etry teaches us that this is accomplished by multiplying one of its 
dimensions by the other. To solve the problem arithmetically, 
then, we have to know the value of the two dimensions expressed 
147 



148 DEFINITIONS 

in numbers, and if these two numbers are 5 and 2, we will multiply 
one by the other and say: 

5 X 2 = 10 

Algebraically, instead, we do not need to know these numeric 
values, but we will call one of the dimensions A, for instance, the 
other B and the surface area S, and we will say that 

S = A xB,or simply: S = A B, 

as, in algebra, the absence of a sign between letters or one number 
and letters means multiplication. 

This is the general way we express in our case the surface area 
of a rectangle, and we call it a formula. To solve this formula or 
equation arithmetically, we have to know the numeric values of 
A and B, substitute them respectively for the letters and multiply 
one by the other. If A = 6, B =3, then: 

5=6X3 = 18 

Analyzing what we have done, we see that to find the value of 
S, we need to know the value of A and B, that is, out of three 
quantities of a formula, we must know two to find out the third. 
Generalizing this special case, we will say that in order to find the 
value of one quantity of a formula, we must know the value of 
all the other quantities. 

To solve an equation, we must know the following rules: 

We can add or subtract, multiply or divide by, the same number 
both members of an equation without altering the equality. 

Let us explain this arithmetically, first. If we have the expression : 

5+4+1 =6+2+2 

or, which is the same: 

10 = 10 

we can add to each member the same number, say, 5, without 
altering the equality; in fact, it will be: 

10 + 5 = 10 + 5 

In the same way, we can subtract the number 3, and we will have: 

10 — 3 - 10 — 3 



DEFINITIONS 149 

Or, multiplying by 4 : 

10 X 4 = 10 X 4 

And, finally, dividing by 2: 

10 10 

2 ~ 2 

In the same way we can raise to power, or extract the root of, 
both members of an equation without altering its equality, as these 
two last cases really amount to special instances of multiplication 
and division. So, it will be: 

10 = 10; 10 2 = 10 2 , that is, 10 X 10 = 10 X 10. 
16 = 16; Vl6 = Vl6, that is, 4=4. 

Using the same process algebraically, we will have the following 
equations: 
If 
adding b, 
subtracting c, 
multiplying by d, 
dividing by e, 

raising to power, a 2 = 

extracting the root, \/a = \/a, \/a = \/a, y/a = \/a 

Suppose now that we have this equation : 

a — b + c = d + e 

and that we add the quantity b to both members, that is: 

a — b + c -{- b = d + e + b 

In the first member of this equation, we see that there is the same 
quantity, b, added and subtracted in the meantime. As the result 
would be zero (+ b — b - 0), we can suppress it and have: 

a + c = d + e +b 

Comparing this equation with the first one, we see that the term b, 
which was in the first member with a negative sign (—), passed 
to the second member with a positive sign (+). 



a = a 




a + b = a + b 




a — c = a — c 




a d = a d 




a a 




— = — 




e e 




a 3 = a 3 , a n = 


a 1 


/a, \/a = v a, 





150 DEFINITIONS 

If we now subtract from both members of the equation 
a — b + c = d + e 
the quantity c, we will have: 

a — 6 + c — c = d + e — c 
As + c — c = 0, it will be: 

a — b = d + e — c 

that is, + c in the first member became — c in the second. 
If we have the equation : 

, c 

a o = - 

d 

and multiply all by d, we will have: 

a b d = - d 
d 

or 

KA d 

a b d = c- 
d 

as - =1, therefore: 
d 

ab d = c X 1, that is: a b d = c 

We see, then, that the quantity d, which was in the second 
member as a divisor, passed to the first member as a multiplicator. 
And, finally, if we have the equation: 

ab = c 
and divide all by b, we have: 

ab c be c c 

— = -, a - = -. o X 1 = -, a = - 

b b b b b' b 

That is, b from multiplicator in the first member became divisor 
in the second. 

We will say, therefore, that we can pass one term from one 
member of an equation to the other by changing its sign without 
altering the equality. 

We understand, now, why from our aerodynamical formula: 

W = C K S F 2 sin a cos a 



DEFINITIONS 151 

we obtain the values of each quantity by passing the others from 
multiplicators in one member to divisors in the other, and in the 
case of the velocity by extracting the square root from both mem- 
bers. 

Altimeter is a modified barometer used for measuring height. 

Anemometer is an instrument for measuring the force and 
velocity of the wind. 

Angle of attack is the angle formed by the chord of the wings 
with the line of flight when the aeroplane climbs or descends. 

Angle of sweepback is the angle formed by the leading edge 
of a wing with the lateral axis of an aeroplane. Best climbing 
angle is approximately halfway between the maximum and optimum 
angles. 

Flying angle of incidence is the angle formed by the neutral line 
of a plane with the line of flight. It is positive when formed above 
the line of flight; negative, when formed below the line of flight; 
zero, when the neutral line is parallel with the line of flight. 

Gliding angle is the angle of attack of an aeroplane descending 
by force of gravity. 

Lateral dihedral angle is the angle formed by two wings when 
they are tipped upward. 

Longitudinal dihedral angle is the angle formed by the pro- 
longation of the chord of the wings with the prolongation of the 
chord of the horizontal stabilizer. If the angle is formed by the 
prolongation of the neutral lines, it is the flying longitudinal dihedral 
angle; if formed by the prolongation of the chords, it is the rigger's 
longitudinal dihedral angle. Rigger's angle of incidence is the angle 
formed by the chord of a plane with the line of thrust. 

Maximum angle of incidence is the greatest angle at which, with 
a given power, surface and weight, horizontal flight can be main- 
tained. 

Minimum angle of incidence is the smallest angle at which, with 
a given power, surface and weight, horizontal flight can be main- 
tained. 

Optimum angle of incidence is the angle at which the lift drift 
ratio is the best. 

Antidrift wire is a wire which acts against the tension of a drift 
wire. There are two kinds of antidrift wires: center section and 
frame antidrift wires. 



152 DEFINITIONS 

Aspect ratio is the proportion of the span to the chord of a plane. 

Aviation is the branch of aeronautics that treats of the gasless 
aircraft. 

Banana oil or varnish is a mixture of acetone and amylacetate 
with liquid celluloid, having a marked banana-like odor. 

Bank is to tilt an aeroplane sideways when turning. 

Barograph is a self-registering barometer, which gives a con- 
tinuous graphic record of the fluctuations of the atmospheric 
pressure. 

Barometer is an instrument which measures the pressure of the 
atmosphere. 

Bay is a compartment in the fuselage or in the wings of a multi- 
plane. 

Bending is the combination of the compression and tension 
stresses. 

Blow torch is a lamp burning gasoline, forced by air pressure 
through a hot, holed tube, to gasify and mix it with air and pro- 
duce an intensely hot, blue flame. 

Cabane is a metallic framework to which are attached the land- 
ing wires of the wings of a monoplane or the upper wings of a multi- 
plane that has no center section. 

Camber is the curvature of a plane. 

Cap strip is the flange of a rib. 

Castellated nut is a nut with grooves in its upper face to receive 
a cotter pin. 

Cavitation is the rarefaction of air produced in the space imme- 
diately in the rear of swiftly revolving propeller blades, due to the 
rapid cleavage of the air by the blades and the relatively slow 
action of the air in closing in behind the moving blades. 

Cellulose is the principal component of all vegetable tissues. 
Cotton and filter paper are almost pure cellulose. 

Center line of pressure is a line running from tip to tip of a wing 
and through which all the air forces acting on the wing may be 
said to act. 

Center of gravity of a body is the point about which all its parts 
are balanced. 

Center of lift is the point of application of the resultant of all 
the lifting forces of an aeroplane. 

Center of pressure is the point at which the whole amount of 



DEFINITIONS 153 

pressure may be concentrated with the same effect as when dis- 
tributed. 

Center of resistance is the point of application of the resultant 
of all the forces of the passive drift acting against the different 
parts of an aeroplane. 

Center of thrust is the point of application of the thrust of the 
propeller. 

Center section is the central structure which connects the upper 
wings of a multiplane. 

Centrifugal force is the reaction of a body against a force that 
is causing it to move in a curved path. 

Centripetal force is a force drawing a body toward the center 
around which it revolves. 

Chord is the straight line drawn from the leading to the trailing 
edge of a plane. 

Clevis pin is a rivet with a hole in the point for the passage of a 
cotter pin. 

Cockpit is the compartment of the fuselage which contains the 
pilot's seat. 

Compass is an instrument by means of which the directive mag- 
netic force of the earth upon a freely suspended magnetic needle 
is utilized to determine horizontal directions in reference to the 
north and the other cardinal points. 

Compression is the stress which tends to crush a body. 

Control lever is a wooden stick or metallic tube to which are 
attached the cables of the ailerons and elevators for controlling 
their motions. 

Controlling plane is a plane designed to control mechanically 
the motions of an aeroplane longitudinally, laterally or directionally. 
There are three kinds of controlling planes: elevators, ailerons and 
rudder. 

Cotter pin is a split key made by bending a half round wire with 
the flat face inside, so as to form an eye at the bend and bring 
together the two halves or leaves, which thus make a round wire 
open in the middle. It is inserted in the hole of a clevis pin to lock 
it safely in place by spreading out the leaves or to lock the nut of 
a bolt provided with an apposite hole at its threaded end. 

Decalage is the difference in the angle of incidence of any two 
planes in the same machine. 



154 DEFINITIONS 

Disk wheel is a wheel stream-lined by covering its spokes with 
cone-shaped sheets of metal, celluloid or doped fabric. 

Dope is a solution of cellulose nitrate or acetate and banana oil 
used to paint the fabric covering of aeroplanes to make it taut and 
airproof. 

Dowel is a round stringer. 

Drift is the horizontal component of the air resistance against 
a plane. 

Active drift is the drift of the lifting planes. 

Passive drift is the drift of all the other parts of an aero- 
plane. 

Total drift is the entire resistance of the air against the machine 
in flight and includes the active drift, the passive drift and the 
skin friction. 

Drift meter is an instrument which indicates the leeway of an 
aeroplane. It consists of a telescope, containing a series of parallel 
hairs with a graduate scale and pointer, mounted vertically to 
enable the pilot to look down upon the ground directly beneath 
him. By turning the telescope so that the hairs are parallel with 
the line of motion, indicated by roads, rivers or other landmarks, 
the exact leeway or drift of the aeroplane is measured by the needle 
of the indicator. 

Drift wire is a wire which supports some part of a machine against 
the drift during flight. There are three kinds of drift wires: the 
wing drift wires, which run from the nose plate to the wings; the 
center section drift wires, which go from the upper longerons to 
the front struts of the center section; and the frame drift wires, 
which are attached between compression ribs inside of the frame 
and are hidden from view by the fabric covering. 

Droop is the increase in the angle of incidence of the ailerons and 
elevators to compensate the decrease which occurs in flight owing 
to the resistance of the air. 

Eddy is a current of air moving in a direction contrary fo the 
main current. 

Efficiency of construction is the ratio of the lifting surface to 
the passive drift surface of an aeroplane. (If the lifting surface is 
200 square feet and the passive drift surface is 10 square feet, the 
efficiency of construction is 200 : 10 = 20.) 

Elevator is a controlling plane hinged horizontally to the rear 



DEFINITIONS 155 

of the horizontal stabilizer of a machine to direct it upwards or 
downwards. 

Empennage is the tail of an aeroplane. 

Equilibrium is the state of balance produced by the mutual 
counter action of two or more forces. Equilibrium is characterized 
by three phases: stable, unstable and indifferent or neutral. A 
body is in a state of stable equilibrium when, being disturbed, it 
tends to return to its previous position; in this state, the center of 
gravity of the body is in its lowest possible place. A body is in 
a state of unstable equilibrium when, being disturbed, it tends to 
move away from its previous position; in this state, the center of 
gravity of the body is in. its highest possible place. A body is in 
a state of indifferent or neutral equilibrium when it keeps its bal- 
ance independently of the position it is put in; in this state, the 
center of gravity of the body is at its center. 

Extension or overhang is the lateral extension of an upper wing 
beyond the span of a lower wing of a multiplane. 

Factor of safety is the ratio of the stress of collapse of a body to 
the maximum stress it is called upon to withstand. 

Fair lead is a short metallic tube with funnel-shaped ends through 
which runs a cable. 

Fairing is the additional material used to stream-line a body. 

Ferrule is a short tubular coupling used for locking a solid wire 
loop. 

Fineness is the ratio of the length to the width of a stream-lined 
body. It is directly proportional to the velocity. 

Fitting is a metallic fixture which connects the joints of different 
pieces of the framework of a machine. 

Flying boat is a hydroaeroplane with a hull in the place of a 
fuselage. 

Flying wire is a wire attached to a point of a wing to prevent it 
from breaking when the machine is in flight. 

Flux is a substance that promotes the fusion of metals, pre- 
vents their oxidation under the action of heat and cleans their 
surface. 

Foot rudder bar is a wooden bar to which are attached the rudder 
control wires. 

Fuselage is the stream-lined main body of an aeroplane to which 
all the other parts are attached. 



156 DEFINITIONS 

Gap is the space between two planes, measured from chord to 
chord. 

Hangar is an aeroplane shed. 

Helicopter is a machine intended to fly by means of horizontal 
screw propellers. 

Horizontal equivalent is the horizontal projection of a body. 

Horizontal stabilizer or fixed tail plane is a plane bolted on the 
upper tail end of the fuselage to give inherent longitudinal stability 
to an aeroplane. 

Hydroaeroplane is a machine with pontoons attached to the 
undercarriage to enable it to rest on and rise from water. 

Hydrochloric acid or muriatic acid is a colorless, corrosive, pun- 
gent gas, exceedingly soluble in water. What is commonly known 
as hydrochloric acid is a strong aqueous solution, colored yellow 
by impurities. It is generally made by the action of strong sul- 
phuric acid on common salt. 

Hydroplane is a flat bottomed, high-powered motor boat, which 
skims at a high speed on the surface of the water. 

Inclinometer is a curved spirit level which indicates the degree 
of inclination of an aeroplane with the horizontal. There are two 
kinds of inclinometers: one determines the angle of attack; the 
other, called laterometer or bank indicator, the angle of bank. 

Inertia is that property of matter by virtue of which it persists 
in its state of rest or of uniform motion in a straight line unless 
it is acted upon by some external force. 

Interference is the detrimental effect produced in the gap by 
the rush of air or wash, which disturbs both the rarefaction of the 
top camber of the lower wing and the compression of the lower 
camber of the upper wing. 

Inspection cover is an accessible stream-lined cover, fastened to 
the upper longerons by hinges on each side, which can easily be 
removed to inspect the control and fuselage wires. 

Keel surface is the total side elevation surface of a machine. 
(Body, wings, struts, wires, wheels, etc.) 

King post is a short mast bolted to a plane for the attachment 
of cables or wires. 

Landing wire is a wire attached to a point of a wing to prevent 
it from breaking when the machine lands or stands on the ground 
or when the wing is subjected to a reversal of load. 



DEFINITIONS 157 

Leading or entering edge is the front edge of a plane. 

Level is an instrument used to determine a horizontal line. 

Lift of an inclined, cambered plane is the vertical component of 
the air resistance against the lower camber, enhanced almost to 
its full power by the rarefaction on the upper camber, which facili- 
tates the lifting force, owing to the difference in the density of the 
two currents of air flowing along the surfaces of the plane. 

Lift drift ratio is the proportion of lift to drift. Considering the 
lifting planes alone, it is the ratio of lift to drift; considering the 
entire machine, it is the ratio of lift to total drift. 

Line of flight is the direction in which flight takes place. It is 
referred to the horizontal, and, therefore, the line of flight is the 
horizontal. 

Longeron is a long wooden piece running longitudinally in the 
fuselage. 

Loop is the doubling of a wire in such a way as to form an eye. 

Margin of lift is the height to which an aeroplane can rise in a 
given time and from a given altitude. 

Margin of power is the power available above that necessary to 
maintain horizontal flight. 

Metric system is the method of measurement based on the meter, 

which theoretically is the part of the quadrant of a 

10,000,000 

terrestrial meridian, and actually is the length of a bar of platinum 

designed to represent that dimension. 

The metric system removes the confusion arising out of the 
excessive diversity of weights and measures prevailing in the world, 
by substituting in place of the arbitrary and inconsistent systems 
actually in use, a single one constructed on scientific principles and 
resting on a natural and invariable standard. 

The unit of length is the meter (30.37 inches) ; the unit of surface, 
the square meter (1550 square inches); the unit of capacity, the 
liter (1.0567 quarts); and the unit of weight, the gram (15.432 
grains troy). 

Each unit has its decimal multiples and submultiples; that is, 
weights and measures ten times larger or ten times smaller than 
the unit of the denomination preceding. 

The prefixes denoting multiples are derived from the Greek lan- 
guage, and are: deca, ten; hecto, hundred; kilo, thousand; and myria, 



158 DEFINITIONS 

ten thousand. Those denoting submultiples are from the Latin 
and are: deci, tenth; centi, hundredth, and milli, thousandth. 

The unit of itinerary measure is the kilometer or 1000 meters 
(0.62138 mile), and the unit of commercial weight is the kilogram 
or 1000 grams (2.205 lb. avoirdupois). 

The meter is divided in ten decimeters, the decimeter in ten 
centimeters, the centimeter in ten millimeters; just as the dollar 
is divided in ten dimes, the dime in ten cents, the cent in ten mills; 
so that it is just as easy to figure out in meters as it is in dollars. 

The abbreviation of kilometer is Km.; square kilometer, Km 2 .; 
kilogram, Kg.; meter, m.; decimeter, dm.; centimeter, cm.; milli- 
meter, mm.; square meter, m 2 ., the exponent being used for its 
submultiples; cubic meter, m 3 ., using the same exponent for the 
submultiples. 

Momentum is the force of motion acquired by a moving body by 
reason of the continuance of its motion. It is measured by the 
product of the mass by the velocity of the body. • 

Monocoque is a tractor fuselage entirely stream-lined with 
three-ply veneer, without longerons, struts or wire bracing. 

Nacelle is the short body of a pusher aeroplane. 

Neutral line is an imaginary line, drawn from the trailing edge 
through the width of a wing, parallel to the line of flight when the 
wing has no lift. 

Nose dive is a nose first plunge of an aeroplane. 

Nose plate is a specially shaped steel sheet which connects the 
front ends of the longerons. 

Ornithopter is a machine intended to fly by means of flapping 
wings. 

Outriggers are long pieces of wood which support the tail of a 
pusher machine. 

Parabola is a curve formed by the intersection of the surface of 
a cone with a plane parallel to one of its sides. 

Parabolic curve is a curve resembling a parabola. 

Plane is a wooden and metallic framework covered with fabric. 

Plumb line is a string with a weight or bob attached to one of 
its ends, used to determine a vertical line. 

Pontoon is a light, airtight, boat-like float. 

Projected propeller surface is the surface projection of a pro- 
peller into a plane perpendicular to its axis. 



DEFINITIONS 159 

Propeller axis is the straight line about which the propeller 
revolves. 

Propeller gap is the distance between the helicoidal paths of 
two consecutive blades. 

Propeller pitch is the distance through which a propeller would 
advance in one revolution, if it moved in an unyielding medium. 
This is the theoretical pitch. The effective pitch is the distance 
actually traveled by the propeller in one revolution. The pitch 
is constant when the angle of the blades varies; it is varying, when 
the angle is constant. 

Propeller pitch angle is the angle at which a propeller blade is 
set. 

Propeller slip is the difference between • the theoretical and ef- 
fective pitch or the distance lost by the propeller in one revolution. 

Propeller thrust is the force impelled by the propeller to the 
point of application. 

Propeller torque is the rotary force of the propeller. It produces 
an opposite rotary motion to the point of application. 

Protractor is an instrument used for measuring angles. 

Pusher machine is an aeroplane with the propeller in the rear. 

Rib is a curved wooden frame used in a wing to give it camber, 
carry the fabric and transfer the lift from the fabric to the spars. 
A rib is composed of three parts: a web and two cap strips. If the 
web is thick and solid, the rib is called a compression rib; if the 
web is thin and lightened by means of holes bored in it, the rib is 
called a camber rib. There is also a false rib, which is a strip of 
wood tacked on the upper front part of a wing to prevent the 
fabric from sinking between the ribs proper. 

Rigging or flying position is the position assumed by the fuselage 
When its engine rails are level both longitudinally and laterally. 

Rivet is a short bolt without a thread. 

Root end of a wing is its thick end to which are attached the 
hinges. 

Rudder is a controlling plane hinged vertically to the rear of a 
machine to steer it to the right or left. 

Rudder post is a steel tube to which is hinged the rudder. 

Safety wire is a fine solid wire used to lock a turnbuckle; or to 
tie aeroplane wires together or to some part of the machine, to 
avoid their falling in the way of the propeller in case of a break. 



160 DEFINITIONS 

Screw propeller is a section of a screw. It screws itself into the 
air and converts a rotary motion into a linear motion. This def- 
inition conforms with the old theory of the propeller; according to 
the new theory, a propeller is a revolving inclined plane. 

Serving is the protective wrapping of a cord or a wire around a 
splice. 

Sextant is an instrument for measuring the angular distance 
between two objects by means of a graduated arc, representing 
the sixth part of a circle, and a double reflection from two 
mirrors. 

Shear stress is the stress that tends to tear a body in such a 
manner as to cause one part to slide over the other. 

Shielding is the protection against the air resistance offered by a 
body on another following in its wake within certain limits and 
producing a decrease in passive drift. 

Side slip is the sideways motion of an aeroplane toward the 
center of a turn as a result of excessive banking. 

Sine. See Trigonometry. 

Skid is a piece of wood, cane or tubing used for supporting or 
allowing to move on it some part of an aeroplane, as the tail, under- 
carriage or wing tips. 

Skid (to skid) is to cause an aeroplane to move sideways 
away from the center of a turn as a result of insufficient 
banking. 

Skin friction is the rubbing of the air against the layer of air 
surrounding the surface of a moving body. 

Span is the length of the main plane of an aeroplane, measured 
from tip to tip, excluding the extension when used. 

Spar is a long piece of wood within a wing to which the ribs are 
attached. 

Stability is the tendency of a body to keep its state of equilibrium. 
In an aeroplane there are three kinds of stabilities: longitudinal or 
in a fore and aft direction; lateral or from port to starboard; di- 
rectional or from right to left. 

Stabilizing plane is a plane that gives inherent stability to a 
machine. There are two stabilizing planes: horizontal and vertical 
stabilizer. 

Stagger is the step disposition of planes, either forward or back- 
ward. 



DEFINITIONS 161 

Stagger and incidence wires are the internal cross bracing 
wires of the wings. 

Stall is to stop the forward motion of an aeroplane through an 
excessive angle of attack. 

Straight edge is a long piece of wood or metal having the edges 
perfectly straight, used to ascertain whether a surface is exactly- 
even. 

Strain is the deformation produced by an overstress. 

Stream-line is the line traced by the successive positions of a 
particle of moving fluid. It is a continuous curve, as a fluid can 
not instantly change its direction of flow without forming a detri- 
mental surface of discontinuity. 

Stress is the load to which a body is subjected. 

Stringer is a long strip of wood running the full length of the 
wing through the web of the ribs to prevent them from rolling 
over. 

Strut is a piece of wood which holds apart two other pieces of 
wood. 

Sweepback is the rearward position assumed by the wings when 
their leading edges form angles with the lateral axis of an aero- 
plane. 

Tail post is the strut at the extreme tail end of the fuselage. 

Tail skid is a piece of wood attached under the tail of a machine 
to carry the weight of its rear portion while on the ground and to 
act as a shock absorber and brake in landing. 

Tail slide is a tail first plunge of an aeroplane. 

Tension is the stress which tends to elongate a body. 

Thrust drift ratio is the proportion of the thrust to the drift of 
a propeller. 

Torsion is a combination of the compression, tension and shear 
stresses. 

Tractor machine is an aeroplane with the propeller in front. 

Trailing edge is the rear edge of a plane. 

Trigonometry is that branch of mathematics which treats of the 
relations of the sides and angles of triangles. 

In studying these relations, the right-angled triangle is taken as 
a base, and the ratio of the sides and hypotenuse taken by two in 
three different ways, forming six ratios in all, are given different 
names. 



162 



DEFINITIONS 



In any right-angled triangle 




A B C, C being the right angle, with reference to the angle A , let 
B C be denoted the opposite side, and A C the adjacent side. Then 
we will have: 

opposite side 



sine A, abbreviated sin A = 



cosine A 



tangent A 
cotangent A 



secant A 



cosecant A 



cos A = 



tan A = 



cot A = 



sec A 



cosec A = 



hypotenuse 
adjacent side 

hypotenuse 
opposite side 
adjacent side 
adjacent side 
opposite side 

hypotenuse 
adjacent side 

hypotenuse 



opposite side 

The numbers which indicate these ratios have already been de- 
termined and tabulated for all angles from one to ninety degrees. 
So that when we want to know the value of these six ratios for a 
given angle, we have to look into the tables of the natural functions 
of angles. As in our calculations we use mostly sines and cosines, 
having only in one instance the use of tangents, we will confine our 
study to them only. 

The sum of the angles of a triangle is equal to two right angles. 
A right angle is ninety degrees (90°). As we take as a base the 
right-angled triangle, it is evident that, C being one right angle, 
A -f B is equal to one right angle. Consequently, if A = 1°, 
B = 89°; A = 2°, B = 88°; A = 44°, B = 46°; A = 45°, B = 45°; 
A = 46°, B = 44°; A = 88°, B = 2°; A = 89°, B = 1°. From 



DEFINITIONS 163 

this, we see that after we reach an angle of 45°, the process is re- 
versed; that is, the sine of an angle of 1° is the cosine of an angle 
of 89°, and vice versa. Therefore, instead of tabulating first all 
the sines of the angles from 1° to 90° and then the cosines from 1° to 
90°, we can tabulate the sines only or, as it is commonly done, we 
can write all the sines from 0° to 45° and the cosines from 90° to 
45°, so arranged that to the sine of an angle corresponds its cosine, 
and vice versa. Where greater precision is required, the tables are 
compiled to give the ratios for fractions of degrees, that is, minutes, 
as one degree is sixty minutes (60'). 

For our calculations, the functions of entire degrees being suffi- 
cient, the following table of sines and cosines will do: 



164 



DIFINITIONS 



Natural Sines and Cosines 



o 


sin 


COS 


° 





sin 


cos 


° 





0.00000 


1 .00000 


90 


23 


0.39073 


0.92050 


67 


1 


0.01745 


0.99985 


89 


24 


0.40674 


0.91355 


66 


2 


0.03490 


0.99939 


88 


25 


0.42262 


0.90631 


65 


3 


0.05234 


0.99863 


87 


26 


0.43837 


0.89879 


64 


4 


0.06976 


0.99756 


86 


27 


0.45399 


0.89101 


63 


5 


0.08716 


0.99619 


85 


28 


0.46947 


0.88295 


62 


6 


0.10453 


0.99452 


84 


29 


0.48481 


0.87462 


61 


7 


0.12187 


0.99255' 


83 


30 


0.50000 


0.86603 


60 


8 


0.13917 


0.99027 


82 


31 


0.51504 


0.85717 


59 


9 


0.15643 


0.98769 


81 


32 


. 52992 


0.84805 


58 


10 


0.17365 


0.98481 


80 


33 


0.54464 


0.83867 


57 


11 


0.19081 


0.98163 


79 


34 


0.55919 


0.82904 


56 


12 


0.20791 


0.97815 


78 


35 


0.57358 


0.81915 


55 


13 


0.22495 


0.97437 


77 


36 


. 58779 


0.80902 


54 


14 


0.24192 


0.97030 


76 


37 


0.60182 


0.79864 


53 


15 


0.25882 


0.96593 


75 


38 


0.61566 


0.78801 


52 


16 


0.27564 


0.96126 


74 


39 


0.62932 


0.77715 


51 


17 


0.29237 


0.95630 


73 


40 


0.64279 


0.76604 


50 


18 


0.30902 


0.95106 


72 


41 


0.65606 


0.75471 


49 


19 


0.32557 


0.94552 


71 


42 


0.66913 


0.74314 


48 


20 


0.34202 


0.93969 


70 


43 


0.68200 


0.73135 


47 


21 


0.35837 


0.93358 


69 


44 


0.69466 


0.71934 


46 


22 


0.37461 


0.92718 


68 


45 


0.70711 


0.70711 


45 




cos 


sin 






cos 


sin 





DEFINITIONS 165 

This is the table of the natural sines and cosines of angles, to 
be distinct from the logarithmic functions, which do not enter in 
our calculations. 

If we want to know the sine and cosine of an angle of 10°, for 
instance, we look in the table for the angle of 10° and we find: sin 
10° = 0.17365, cos 10° = 0.98481. If, instead, we look for the 
sine and cosine of an angle of 80°, we find: sin 80° = 0.98481, cos 
80° = 0.17365. In this way, we will be able to find the sine and 
cosine of any angle. 

If, as a result of our calculations, we find the sine of an angle and 
we want to know its value in degrees, we look for this sine in the 
tables and see what degree corresponds to it; but if we do not find 
a sine exactly equal to the one we are looking for, it means that the 
angle is not expressed by an entire number of degrees, and we 
have to look for it in more detailed tables. 

Suppose, for instance, that we want to know what angle in 
degrees corresponds to the sine 0.105. In the table, we find that 
the nearest approach to it is sin 6° = 0.10453; therefore, the degree 
of our angle is between 6° and 7°; but, evidently, much nearer to 
6° than it is to 7°. And if we look for it in a more detailed table, 
we find our angle expressed in degrees and factions of a degree or 
minutes. 

Turnbuckle is a coupling with a barrel and a right hand and a 
left hand eye screw or shank used to regulate the length and tension 
of wires. The right hand screw shank, which sometimes is split or 
forked, is always attached to a fitting, while the left hand screw 
shank is attached to the wire. This is done to determine the turn- 
ing direction of the barrel in tightening or loosening a wire, as, in 
this case, the operation is that of an ordinary right hand screw nut. 
The come and go is the distance the shanks can be screwed in or out. 

Undercarriage is that part of an aeroplane designed to support 
it when at rest, to absorb the shock of landing and to give clearance 
to the propeller and wings. 

Veneer is a thin layer of wood. 

Vertical stabilizer or fin is a triangular plane bolted at the upper 
part of the horizontal stabilizer to give inherent directional stability 
to an aeroplane. 

Volplane is a glide. 

Wash in is an increase in the angle of incidence. 



166 DEFINITIONS 

Wash out is a decrease in the angle of incidence. 

Web is the central part of a rib. 

Wind screen is a shield placed in front of the cockpit to protect 
the aviator from the effect of the wind. 

Wind tunnel is a tube through which air is forced or drawn by 
means of rotating fans. 

Wing is a fabric covered, cambered, wooden and metallic frame. 

Wing tip is the extreme thin end of a wing opposite the root end. 



INDEX 



Acetone, 147 

Ackerman wheel, 40 

Active drift, 14, 154 

Aeroplane 14, 147 

Aerotelephone, 118 

Aileron, 44, 70, 147 ■ 

Aileron control, 50, 53 

Aileron droop, 78 

Air resistance, 1, 3, 14, 16, 134, 

Air speed meter, 147 

Air spill, 12, 139 

Algebra, 147 

Altimeter, 151 

Aluminum, 62 

Anemometer, 151 

Angle of attack, 151 

Angle of incidence, 3, 9, 10, 77, 

Angle of sweepback, 28, 151 

Antidrift wire, 42, 43, 151 

Ascending, 122 

Ash, 61 

Aspect ratio, 11, 151 

Assembling, 70 

Assembling order, 34 

Aviation, 1, 151 

Axle, 38, 101 

B 

Balance wire, 50 
Banana oil, 68, 152 
Bank, 152 
Bank indicator, 156 
Barograph, 152 
Barometer, 152 
Baseball stitch, 113 



135 



135 



Battens, 55, 56 

Bay, 152 

Bending, 58, 81, 152 

Biplane, 14 

Bird's muscular power, 5 

Blow torch, 107, 152 

Bolts, 66, 71 

Bottom rudder, 123 

Bracing wires, 42, 47, 72 

Brake, 41 

Brushes, 69 

Bulkheads, 54, 55 



Cabane, 45, 46, 152 
Camber, 152 
Camber ribs, 44, 159 
Cambered planes, 4, 5, 10, 138 
Cap strip, 44, 152 
Castellated nut, 66, 152 
Cavitation, 90, 152 
Cedar, 61 
Cellulose, 152 
Cellulose nitrate, 68 
Center line of pressure, 152 
Center of gravity, 18, 19, 20, 21, 

22, 29, 42, 152 
Center of lift, 18, 29, 152 
Center of pressure, 10, 21, 22, 136, 

152 
Center of resistance, 18, 29, 153 
Center of thrust, 18, 29, 153 
Center section, 42, 70, 75, 153 
Center section panel, 42 
Centrifugal force, 20, 153 
Centripetal force, 153 



167 



168 



INDEX 



Chord, 11, 153 

Circular flight, 20 

Cleaning, 100 

Clevis pin, 66, 153 

Cockpit, 36, 153 

Coefficient of curvature, 139 

Coefficient of resistance, 134 

Compass, 153 

Compensating wire, 53 

Compression, 58, 153 

Compression rib, 44 

Control cable, 63, 101 

Control column, 50 

Control lever, 153 

Control wire, 50, 72 

Controlling planes, 81, 82, 153 

Controls, 49, 80, 102, 121, 123 

Cord stay, 63 

Cotter pin, 66, 71, 153 

Cotton, 68 

Cowl, 37 

Cowling, 36 

Cross bracing wires, 34, 36, 38, 42, 

43,73 
Curtiss boss, 98 



Decalage, 24, 153 
Degree of curvature, 8 
Directional stability, 22 
Disk wheels, 39, 154 
Dope, 68, 113, 154 
Doping, 69 
Dowels, 44, 154 
Drain holes, 54, 55 
Drift, 2, 5, 7, 136, 138, 140, 154 
Drift meter, 154 
Drift wires, 42, 43, 46, 154 
Droop, 154 
Drum, 50 
Dual control, 53 

Dual control system of instruc- 
tion, 117, 118 



E 

Eddy, 154 

Effective area, 11, 139 
Efficiency of construction, 154 
Elementary flying, 120 
Elevators, 45, 79, 80, 123, 154 
Elevators control, 51, 53, 72 
Elevators droop, 80 
Empennage, 44, 72, 78, 155 
Engine rails, 34, 35, 61, 82 
Engine rails support, 34, 72 
Engine section, 36, 37 
Equation, 147 
Equilibrium, 17, 155 
Extension, 14, 155 



Fabric, 67, 101, 113 

Factor of safety, 59, 60, 155 

Fairing, 36, 155 

Fair lead, 66, 155 

False ribs, 43, 44, 159 

Ferrule, 64, 155 

Ferrule and loop, 65, 104 

Figure 8 turns, 122 

Fineness, 15, 155 

Fittings, 34, 35, 63, 101, 103, 155 

Flat planes, 1 

Flight hints, 116 

Flutter, 97 

Flux, 105, 106, 155 

Flying angle of incidence, 10, 151 

Flying boat, 56, 155 

Flying wires, 45, 47, 71, 155 

Foot rudder bar, 50, 155 

Forced landing, 102 

Formula, 147 

Formula of A H P, 140, 141 

Formula of center of pressure, 136 

Formula of drift, 137 

Formula of E H P, 139 

Formula of H P, 138, 139 



INDEX 



169 



Formula of lift, 137, 142 
Formula of passive drift, 140 
Formula of sin a cos a, 143, 144 
Formula of S, 143 
Formula of T H P, 141 
Formula of V, 143 
Formula of W, 143 
Formulae in British Units, 145 
Furnace, 110 
Fuselage, 34, 37, 70, 72, 155 



Gap, 12, 88, 156 
Glider, 8 
Gliding, 29, 122 
Gliding angle, 29, 151 
Gliding path, 30 
Gnome boss, 98 



Hand holes, 54, 55, 81 

Hangar, 156 

Helicopter, 8, 141, 156 

High aspect ratio, 12 

Higher wing, 125 

Hinges, 43 

Holes in fabric, 114 

Holes in wood, 103 

Horizontal component, 2 

Horizontal equivalent, 7, 27, 156 

Horizontal projection, 7 

Horizontal stabilizer, 24, 44, 45, 
72, 78, 156 

Hydraulic pneumatic shock ab- 
sorbers, 40 

Hydroaeroplane, 54, 56, 156 

Hydrochloric acid, 106, 156 

Hydroplane, 156 



Inclined plane, 7, 135 
Inclinometer, 156 



Inertia, 156 
Inherent stability, 23 
Inspection, 100 
Inspection cover, 156 
Interference, 12, 88, 156 
Interplane struts, 47 
Irish linen, 67 

K 

Keel surface, 57, 156 
King post, 47, 156 
Kite, 1 



Landing, 122 

Landing wires, 45, 47, 71, 156 

Lateral dihedral angle, 26, 151 

Lateral stability, 19 

Laterometer, 156 

Leading edge, 5, 9, 43, 61, 70, 75, 

76, 157 
Left side of aeroplane, 72 
Level, 81, 157 
Lift, 2, 5, 7, 11, 12, 13, 136, 137, 

140, 157 
Lift drift ratio, 7, 157 
Lifting tail, 24 
Line, 81 

Line of flight, 9, 157 
Locking arrangement, 101 
Locking wires, 64 
Longerons, 34, 61, 157 
Longitudinal dihedral angle, 24, 

76, 151 
Longitudinal stability, 18 
Loop, 65, 112, 129, 157 
Low aspect ratio, 12 
Lower wing, 125 

M 

Mahogany, 61 
Maintenance, 100 



170 



INDEX 



Margin of lift, 157 

Margin of power, 157 

Materials of construction, 57 

Maxim angle of incidence, 151 

Metal, 62 

Metallic sheets, 67 

Methods of instruction, flying, 116 

Metric system, 157 

Minimum angle of incidence, 151 

Momentum, 158 

Monel metal, 62 

Monocoque, 37, 158 

Monoplane, 14 

Moving parts of aeroplane, 101 

Multiplane, 14 

N 

Nacelle, 38, 158 

Negative angle of incidence, 10 

Negative stagger, 14 

Neutral line, 9, 158 

Neutral position of controls, 51 

Non-lifting tail, 26 

Non-skid fin, 57 

Nose dive, 158 

Nose plate, 34, 36, 158 

Nuts, 66, 81 

O 

Oleo pneumatic shock absorbers, 
40 

One-seat machine method of in- 
struction, flying, 117 

Optimum angle of incidence, 151 

Ornithopter, 5, 141, 142, 158 

Outriggers, 49, 158 

Overhang, 76 



Paint, 103 

Parabola, 8, 158 

Parabolic curve, 8, 158 

Passive drift, 14, 16, 140, 145, 154 



Patching, 113, 114 

Phillip's coefficient, 16 

Picketing, 102 

Pins, 71 

Plane, 158 

Planing fins, 55 

Plumb line, 74, 158 

Plywood, 60 

Pontoons, 54, 56, 57, 158 

Positive angle of incidence, 10 

Positive stagger, 14 

Power plant, 48 

Pressed steel, 103 

Propeller, 14, 72, 83, 102, 141, 160 

Propeller alignment, 99 

Propeller angle of pitch, 84, 87, 92, 

96, 159 
Propeller apparent slip, 91 
Propeller axis, 159 
Propeller balance, 95 
Propeller balance error, 96 
Propeller blade joints, 97 
Propeller blade length, 97 
Propeller blade straightness, 97 
Propeller blade warpage, 96 
Propeller blade width, 97 
Propeller bolt holes, 97 
Propeller boss, 97 
Propeller developed circumference 

of revolution, 86 
Propeller diameter, 89 
Propeller effective pitch, 84, 89 
Propeller efficiency, 139 
Propeller gap, 159 
Propeller hub, 85 
Propeller hub holes, 97 
Propeller manufacture, 93 
Propeller, metallic, 94 
Propeller metallic tips, 95 
Propeller mounting, 99 
Propeller negative slip, 91 
Propeller pitch, 84, 93, 159 
Propeller pitch line, 86, 87 



INDEX 



171 



Propeller pitch ratio, 89 
Propeller position, 91 
Propeller problems, 92 
Propeller projected surface, 158 
Propeller slip, 84, 159 
Propeller test, 96 
Propeller thrust, 159 
Propeller thrust drift ratio, 89, 161 
Propeller torque, 31, 79, 90, 159 
Propeller triangle of pitch, 86 
Propeller, wooden, 94 
Protractor, 159 
Punctures in tires, 115 
Pusher machine, 48, 49, 159 

R 

Radius of glide, 30 

Radius rod, 38, 41 

Reenforcing struts, 34, 55 

Repairs, fabric, 102 

Repairs, metal, 103 

Repairs, rubber, 115 

Repairs, wood, 102 

Ribs, 43, 61, 159 

Rigger's angle of incidence, 10 

Rigging, 70 

Rigging care and faults, 80 

Rigging position, 70, 72, 159 

Right side of aeroplane, 72 

Rivet, 66, 159 

Roll, 131 

Root end, 68, 159 

Rubber shock absorbers, 39, 101 

Rudder, 22, 44, 123, 159 

Rudder control, 51, 53, 72, 79 

Rudder post, 34, 36, 101, 159 



Safety wire, 159 
Sagging, 21 
Screws, 67 
Sea Island cotton, 68 



Self -instruction, flying, 116 

Semilifting tail, 25 

Serving, 66, 105, 160 

Sextant, 160 

Sharp turns, 122 

Shear stress, 58, 160 

Shielding, 16, 160 

Shock absorber fittings, 38 

Side slip, 125, 160 

Silk, 68 

Sine, 160 

Skid, 160 

Skin friction, 16, 134, 160 

Slight climbing turns, 122 

Slight climbs, 122 

Slight deviations from straight 

flight, 121 
Slight sideways motions, 122 
Soap, 100 
Solder, 105 
Soldering, 105 
Soldering iron, 111 
Solid wire, 63 
Solo flying, 122 
Span, 11, 160 
Spar varnish, 69 
Spars, 43, 61, 160 
Spin, 126 
Spiraling, 122 
Spliced loop, 66 
Spokes, 101 
Spreader, 38, 39 
Spruce, 61 
Stability, 17, 160 
Stability plane, 160 
Stagger, 14, 75, 78, 160 
Stagger and incidence wires, 47, 

75, 161 
StaU, 161 
Steel, 62 

Steel tubing, 62, 63 
Steeper climbs and descents, 122 
Step, 54, 55 



172 



INDEX 



Stick, 52 

Stick control, 52, 54, 119 

Straight edge, 81, 161 

Straight flight, 19, 121 

Strain, 58, 161 

Strand stay, 63 

Stranded wire, 63 

Stream-line, 4, 15, 161 

Strength of materials, 58 

Stress, 58, 161 

Stringers, 43, 44, 161 

Strut, 13, 34, 35, 38, 42, 61, 70, 71, 

73, 101, 161 
Stunts, 122 
Superposed planes, 12 
Sweepback, 28, 161 



Table of sines and cosines, 164 

Tacks, 67 

TaH, 24 

Tail post, 34, 35, 161 

Tail section, 36 

Tail skid, 34, 36, 161 

Tail skid post, 101 

Tail slide, 129, 161 

Tandem planes, 3, 4 

Taxying, 119 

Tears in fabric, 113 

Tension, 58, 161 

Thimble, 65 

Thimble and loop wrapped and 

soldered, 65, 105 
Three-ply veneer, 43 
Tires, 39 
Tools, 81 
Top rudder, 123 
Torsion, 58, 161 
Total drift, 154 
Tractor aeroplane, 48, 161 
Trailing edge, 9, 43, 61, 71, 75, 81, 

161 
Trigonometry, 161 

Printed in the United 



Triplane, 14 

Truing, 72 

Turnbuckle, 34, 36, 63, 81, 165 

Turtleback, 37 

Twin-motor machine, 48 

U 

Undercarriage, 38, 41, 70, 74, 165 



Veneer, 43, 60, 165 

Vent pipe, 54, 55 

Vertical bank, 123 

Vertical component, 2 

Vertical equivalent, 7 

Vertical projection, 7, 79 

Vertical stabilizer, 22, 28, 44, 45, 

72, 78, 165 
Volplane, 165 

W 

Walnut, 61 

Wash in, 31, 78, 165 

Wash out, 31, 78, 166 

Washers, 66, 103 

Web, 44, 166 

Wheel control, 50, 54, 119 

Wheels, 38, 39 

White pine, 61 

Wind screen, 166 

Wind tunnel, 166 

Wing covering, 68 

Wing tip, 43, 166 

Wings, 43, 70, 75 

Wire test, 103 

Wires, 45, 63, 73, 76, 81, 101 

Wood, 60 

Wrapped and soldered loop, 65, 105 

Wrenches, 81 



Zero angle of incidence, 3 
Zero stagger, 14 

Statea of America 



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The Beginnings of Knowledge 

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Weights and Measures 

The Beginnings of Science 

The Beginnings of Experi- 
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The Realities of Science 

The Molecular Composition of 
Matter 

The Electron 

Energy 

Some Uses of Mathematics 

Rates 

Force, a Space Rate of Energy 



Molecular Motions and Tem- 
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Motions of Electrons 

The Interactions of Moving 
Electrons 

The Continuity and Corre- 
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Molecular Mixtures 

Electrolytic Dissociation 

Equilibria and Their Displace- 
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Molecular Magnitudes 

Molecular Energy 

Electronic Magnitudes 

Index 



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